LIFE LEXICON
  Release 29, 2018 July 2
  ASCII version

INTRODUCTION
  This is a lexicon of terms relating to John Horton Conway's
Game of Life.  It is also available in single-page and multipage
HTML versions.
  This lexicon was originally compiled between 1997 and 2006 by
Stephen A. Silver, and was updated in 2016-18 by Dave Greene and David
Bell.  See below for additional credits.
  The latest versions of this lexicon (both HTML and ASCII) can be
found at the Life Lexicon Home Page, http://conwaylife.com/ref/lexicon/.

CREDITS
  The largest single source for the early versions of this lexicon was
a glossary compiled by Alan Hensel "with indispensable help from John
Conway, Dean Hickerson, David Bell, Bill Gosper, Bob Wainwright, Noam
Elkies, Nathan Thompson, Harold McIntosh, and Dan Hoey".
  Other sources include the works listed in the bibliography at the
end of this lexicon, as well as pattern collections by Alan Hensel and
David Bell (and especially Dean Hickerson's file stamp.l in the latter
collection), and the web sites of Mark Niemiec, Paul Callahan, Achim
Flammenkamp, Robert Wainwright and Heinrich Koenig.  Recent releases
also use a lot of information from Dean Hickerson's header to his
1995 stamp file (http://conwaylife.com/ref/DRH/stamps.html).
  Most of the information on recent results is from the discoverers
themselves, or from Nathaniel Johnston's excellent resources at
http://www.conwaylife.com, including both the LifeWiki and the
discussion forums.
  The following people all provided useful comments on earlier releases
of this lexicon:  David Bell, Nicolay Beluchenko, Johan Bontes, Daniel
Collazo, Scot Ellison, Nick Gotts, Ivan Fomichev, Dave Greene, Alan
Hensel, Dean Hickerson, Dieter Leithner, Mark Niemiec, Gabriel Nivasch,
Andrzej Okrasinski, Arie Paap, Peter Rott, Chris Rowett, Tony Smith,
Ken Takusagawa, Andrew Trevorrow, Malcolm Tyrrell, and the
conwaylife.com forum users with the handles 'thunk' and 'Apple Bottom'.

  The format, errors, use of British English and anything else you
might want to complain about are by Stephen Silver - except that for
post-Version 25 definitions, everything besides the British English
may well be Dave Greene's fault instead.

COPYING
  This lexicon is copyright (C) Stephen Silver, 1997-2018.  It may be
freely copied, modified and distributed under the terms of the Creative
Commons Attribution-ShareAlike 3.0 Unported licence (CC BY-SA 3.0),
as long as due credit is given.  This includes not just credit to those
who have contributed in some way to the present version (see above),
but also credit to those who have made any modifications.

LEXICOGRAPHIC ORDER
  I have adopted the following convention: all characters (including
spaces) other than letters and digits are ignored for the purposes of
ordering the entries in this lexicon.  (Many terms are used by some
people as a single word, with or without a hyphen, and by others as two
words.  My convention means that I do not have to list these in two
separate places.  Indeed, I list them only once, choosing whichever
form seems most common or sensible.)  Digits lexicographically precede
letters.

FORMAT
  The format used in the ASCII version of this lexicon is loosely
based on that of the Jargon File.  In particular, the keywords are
enclosed in colons and selected references to them are enclosed in
curly brackets.  The curly brackets will not be of much use unless
you have a programmable text editor, in which case you could program
it to jump from a reference to the corresponding definition when you
hit a certain key.  (The file lifelex.el, which you should have
received with this lexicon, provides such a facility for GNU Emacs.)
If you don't want the curly brackets you can safely remove them with
two find and replace operations, since they are not used for any other
purpose in this file.  The colons are more generally useful.  For
example, a search for ":foo" will take you straight to the definition
of the first word beginning with "foo" (or at least it would if there
were any).
  The diagrams in this lexicon are in a very standard format.  You
should be able to simply copy a pattern, paste it into a new file and
run it in your favourite Life program.  Of course if you use Golly
(http://golly.sf.net) then you can paste the pattern directly into the
program.  If you view this lexicon in GNU Emacs and use lifelex.el then
you should be able to load a pattern into your Life program with a
single keypress, without needing to copy or paste.
  The diagrams use an asterisk to represent a live cell.  If this looks
ugly with the font you use then you can change to O or o with a global
replace.  I have restricted myself to diagrams of size 64x64 or less.
  Most definitions that have a diagram have also some data in brackets
after the keyword.  Oscillators are marked as pn (where n is a positive
integer), meaning that the period is n (p1 indicates a still life).
Wicks are marked in the same way but with the word "wick" added.  For
spaceships the speed (as a fraction of c, the speed of light), the
direction and the period are given.  Fuses are marked with speed and
period and have the word "fuse" added.  Wicks and fuses are infinite in
extent and so have necessarily been truncated, with the ends stabilized
wherever practical.

SCOPE
  This lexicon covers only Conway's Life, and provides no information
about other cellular automata.  David Bell has written articles on
two other interesting cellular automata: HighLife (which is similar
to Life, but has a tiny replicator) and Day & Night (which is very
different, but exhibits many of the same phenomena).  These articles
can be found on his website (http://tip.net.au/~dbell/).

ERRORS AND OMISSIONS
  If you find any errors (including typos) or serious omissions, then
please email b3s23life[at]gmail.com with the details.  As of mid-2018
this email address is monitored by Dave Greene.

NAMES
  When deciding whether to use full or abbreviated forms of forenames
I have tried, wherever possible, to follow the usage of the person
concerned.

QUOTE
  Every other author may aspire to praise; the lexicographer can only
hope to escape reproach.  -- Samuel Johnson, 1775

DEDICATION
  This lexicon is dedicated to the memory of Dieter Leithner, who died
on 26 February 1999.

-----------------------------------------------------------------------

:0hd Demonoid:  See {Demonoid}.

:101: (p5)  Found by Achim Flammenkamp in August 1994.  The name was
   suggested by Bill Gosper, noting that the {phase} shown below
   displays the period in binary.
	....**......**....
	...*.*......*.*...
	...*..........*...
	**.*..........*.**
	**.*.*..**..*.*.**
	...*.*.*..*.*.*...
	...*.*.*..*.*.*...
	**.*.*..**..*.*.**
	**.*..........*.**
	...*..........*...
	...*.*......*.*...
	....**......**....

:10hd Demonoid:  See {Demonoid}.

:119P4H1V0: (c/4 orthogonally, p4)  A {spaceship} discovered by Dean
   Hickerson in December 1989, the first spaceship of its kind to be
   found. Hickerson then found a small {tagalong} for this spaceship
   which could be attached to one side or both. These three variants of
   119P4H1V0 were the only known c/4 orthogonal spaceships until July
   1992 when Hartmut Holzwart discovered a larger spaceship, 163P4H1V0.
	.................................*.
	................*...............*.*
	......*.*......*.....**........*...
	......*....*....*.******....**.....
	......*.********..........*..*.***.
	.........*.....*.......****....***.
	....**.................***.*.......
	.*..**.......**........**..........
	.*..*..............................
	*..................................
	.*..*..............................
	.*..**.......**........**..........
	....**.................***.*.......
	.........*.....*.......****....***.
	......*.********..........*..*.***.
	......*....*....*.******....**.....
	......*.*......*.....**........*...
	................*...............*.*
	.................................*.

:1-2-3: (p3)  Found by Dave Buckingham, August 1972. This is one of only
   three essentially different p3 {oscillator}s with only three cells in
   the {rotor}.  The others are {stillater} and {cuphook}.
	..**......
	*..*......
	**.*.**...
	.*.*..*...
	.*....*.**
	..***.*.**
	.....*....
	....*.....
	....**....

:1-2-3-4: (p4)  See also {Achim's p4}.
	.....*.....
	....*.*....
	...*.*.*...
	...*...*...
	**.*.*.*.**
	*.*.....*.*
	...*****...
	...........
	.....*.....
	....*.*....
	.....*.....

:135-degree MWSS-to-G:  The following {converter}, discovered by
   Matthias Merzenich in July 2013.  It accepts an {MWSS} as input, and
   produces an output {glider} travelling at a 135-degree angle relative
   to the input direction.
	......**......
	......*.*.**.*
	........*.*.**
	........**....
	..............
	..............
	.*****.....**.
	*....*.....**.
	.....*........
	*...*.........
	..*...........

:14-ner:  = {fourteener}

:17c/45 spaceship:  A {spaceship} travelling at seventeen forty-fifths
   of the {speed of light}.  This was the first known {macro-spaceship}
   speed.  See {Caterpillar} for details.

:180-degree kickback:  The only other two-{glider} collision besides the
   standard {kickback} that produces a clean output glider with no
   leftover {ash}.  The 180-degree change in direction is occasionally
   useful in {glider synthesis}, but is rarely used in {signal}
   circuitry or in {self-supporting} patterns like the {Caterpillar} or
   {Centipede}, because 90-degree collisions are generally much easier
   to arrange.
	.*.
	*..
	***
	...
	...
	.**
	*.*
	..*

:1G seed:  See {seed}.

:(2,1)c/6 spaceship:  A {knightship} that travels obliquely at the
   fastest possible speed.  To date the only known example of a
   spaceship with this velocity is {Sir Robin}.

:(23,5)c/79 Herschel climber:  The following glider-supported
   {Herschel climber} reaction used in the {self-supporting} {waterbear}
   {knightship}, which can be repeated every 79 ticks, moving the
   {Herschel} 23 cells to the right and 5 cells upward, and releasing
   two {glider}s to the northwest and southwest.  As the diagram shows,
   it is possible to substitute a loaf or other {still life}s for some
   or all of the support gliders.  This fact is used to advantage at the
   front end of the waterbear.
	...............*.*...............*..
	...............**...............*.*.
	................*...............*..*
	.................................**.
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	*...................................
	*.*.................................
	***.................................
	..*.................................

:24-cell quadratic growth:  A 39786x143 {quadratic growth} pattern found
   by Michael Simkin in October 2014, two days after
   {25-cell quadratic growth} and a week before
   {switch-engine ping-pong}.

:25-cell quadratic growth:  A 25-cell quadratic growth pattern found by
   Michael Simkin in October 2014, with a bounding box of 21372x172. It
   was the smallest-population quadratic growth pattern for two days,
   until the discovery of {24-cell quadratic growth}. It superseded
   {wedge}, which had held the record for eight years.  See
   {switch-engine ping-pong} for the lowest-population
   {superlinear growth} pattern as of July 2018, along with a list of
   the record-holders.

:25P3H1V0.1: (c/3 orthogonally, p3)  A {spaceship} discovered by Dean
   Hickerson in August 1989.  It was the first c/3 spaceship to be
   discovered. In terms of its 25 cells, it is tied with {25P3H1V0.2} as
   the smallest c/3 spaceship.  Unlike 25P3H1V0.2, it has a population
   of 25 in all of its phases, as well as a smaller bounding box.
	.......**.*.....
	....**.*.**.***.
	.****..**......*
	*....*...*...**.
	.**.............
   Martin Grant discovered a glider synthesis for 25P3H1V0.1 on 6
   January 2015.

:25P3H1V0.2: (c/3 orthogonally, p3)  A {spaceship} discovered by David
   Bell in early 1992, with a minimum of 25 cells - the lowest number of
   cells known for any c/3 spaceship.  A note in
   {Spaceships in Conway's Life} indicates that it was found with a
   search that limited the number of live cells in each column, and
   possibly also the maximum cross-section (4 cells in this case).  See
   also {edge-repair spaceship} for a very similar c/3 spaceship with a
   minimum population of 26.
	..........*.....
	........***.***.
	.......**......*
	..*...*..*...**.
	.****...........
	*...*...........
	.*.*..*.........
	.....*..........
   In December 2017 a collaborative effort found a 26-glider synthesis
   for this spaceship.

:26-cell quadratic growth:  = {wedge}.

:295P5H1V1: (c/5 diagonally, p5) The first {spaceship} of its type to be
   discovered, found by Jason Summers on 22 November 2000.
	.............**.....................................
	.....**....**.*.*...................................
	....***....****.....................................
	...**......**.....*.................................
	..**..**...*..*..*..................................
	.**.....*.......*..**...............................
	.**.*...****........................................
	....*...**..**.*....................................
	.....***....*.*.....................................
	......**...**..*....................................
	......*.....*.......................................
	.****.*..*..*...*...................................
	.***...*****..*******.*.............................
	*.*....*..........*..**.............................
	***.*...*...*.....***...............................
	.......*.*..*.......**..............................
	.*...*.....**........**..*.*........................
	....*.......*........***.*.***......................
	...*........***......*....*.........................
	.....*......*.*.....*.*.............................
	.....*......*.**...*....*...........................
	.............*.****...*.....*..*....................
	............**..**.*.*...*.***......................
	.................*......*..***...***................
	....................*..*......**....................
	................**....*..*..........**..............
	..................*.............*...*...............
	................**....**........*...................
	.................*...***........*.*.*.*.............
	.................*....**........*.....**............
	........................*........*..***.............
	.....................*..*........*........*.........
	..........................****........**...*........
	.......................*......**......**...*........
	.......................*....*............*..........
	.......................*...............*............
	.........................**.*.*.......*..*..........
	.........................*....*.........***.........
	............................***.**..*...*...*.**....
	.............................*..**.*.....*...*..*...
	.....................................**..*...*......
	..................................*.**.**.*..**...*.
	...............................*.....*...*.......*.*
	................................**............**...*
	......................................*.......**....
	.......................................***...**..*..
	......................................*..*.***......
	......................................*....**.......
	.......................................*............
	..........................................*..*......
	.........................................*..........
	..........................................**........

:2c/3:  Two thirds of the speed of light - the speed of signals in a
   {2c/3 wire} or of some {against the grain} {negative spaceship}
   signals in the {zebra stripes} {agar}, and also the speed of
   {burn}ing of the {blinker fuse} and the {bi-block fuse}.

:2c/3 wire:  A {wire} discovered by Dean Hickerson in March 1997, using
   his {dr} {search program}.  It supports {signal}s that travel through
   the wire diagonally at two thirds of the {speed of light}.
	......*..*.......................................
	....******.......................................
	...*.............................................
	...*..******.....................................
	**.*.*.*....*....................................
	**.*.*.******....................................
	....**.*.......*.................................
	.......*..******.................................
	.......*.*.......................................
	......**.*..******...............................
	.........*.*......*..............................
	.........*.*..*****..............................
	..........**.*.......*...........................
	.............*..******...........................
	.............*.*.................................
	............**.*..******.........................
	...............*.*......*........................
	...............*.*..*****........................
	................**.*.......*.....................
	...................*..******.....................
	...................*.*...........................
	..................**.*..******...................
	.....................*.*......*..................
	.....................*.*..*****..................
	......................**.*.......*...............
	.........................*..******...............
	.........................*.*.....................
	........................**.*..******.............
	...........................*.*......*............
	...........................*.*..*****............
	............................**.*.......*.........
	...............................*..******.........
	...............................*.*...............
	..............................**.*..******.......
	.................................*.*......*......
	.................................*.*..*****......
	..................................**.*.......*...
	.....................................*..******...
	.....................................*.*.........
	....................................**.*..******.
	.......................................*.*......*
	.......................................*.*..***.*
	........................................**.*...*.
	...........................................*..*..
	...........................................*.*...
	..........................................**.*.*.
	..............................................**.
     Each 2c/3 signal is made up of two half-signals that can be
   separated from each other by an arbitrary number of {tick}s.
     Considerable effort has been spent on finding a way to turn a 2c/3
   signal 90 or 180 degrees, since this would by one way to prove Life
   to be {omniperiodic}.  There is a known 2c/3 converter shown under
   {signal elbow}, which converts a standard 2c/3 signal into a
   double-length signal.  This is usable in some situations, but
   unfortunately it fails when its input is a double-length signal, so
   it can't be used to complete a loop.
     Noam Elkies discovered a glider synthesis of a reaction that can
   repeatably insert a signal into the upper end of a 2c/3 wire.  See
   {stable pseudo-Heisenburp} for details.  On 11 September 2017, Martin
   Grant reduced the input reaction to five gliders, or three gliders
   plus a {Herschel}.  With the Herschel option the {recovery time} is
   152 ticks.
     See also {5c/9 wire}.

:2c/5 spaceship:  A {spaceship} travelling at two fifths of the
   {speed of light}.  The only such spaceships that are currently known
   travel orthogonally.  Examples include {30P5H2V0}, {44P5H2V0},
   {60P5H2V0}, and {70P5H2V0}.  As of June 2018, only 30P5H2V0 and
   60P5H2V0 have known {glider synthesis} {recipe}s.

:2c/7 spaceship:  A {spaceship} travelling at two sevenths of the
   {speed of light}.  The only such spaceships that are currently known
   travel orthogonally.  The first to be found was the {weekender},
   found by David Eppstein in January 2000.  See also
   {weekender distaff}.

:2 eaters:  = {two eaters}

:2-engine Cordership:  The smallest known Cordership, with a minimum
   population of 100 cells, discovered by Aidan F. Pierce on 31 December
   2017.  Luka Okanishi produced a 9-glider synthesis of the spaceship
   on the same day.
	............*............................
	............*.....***....................
	...........*.*...**..*...................
	............*...*.....*..................
	............*...*........................
	.................*..**...................
	..................**...........**........
	...............................**........
	.........................................
	.........................................
	.........................................
	.........................................
	.........................................
	.........................................
	.***...................................**
	.***.....................*.............**
	..*............**.........**.............
	...**.........*.***........**............
	....*.........*...*..........*...........
	...*...........**.*.....*****............
	................*..........*.............
	.........................................
	.........................................
	.**......................................
	.**......................................
	..*......................................
	..*......................................
	.*.*.....................................
	*........................................
	.*..**...................................
	..*...*..................................
	....**...................................
	....*....................................
	.........................................
	.........................................
	.........................................
	.........................................
	.........................................
	.........................................
	......**.................................
	......**.................................
	...................*.....................
	...................***...................
	....................**...................
	....................*....................
	.........................................
	..................**.*...................
	..................****...................
	....................**...................

:2-glider collision:  Two gliders can react with each other in many
   different ways, either at right angles, or else head-on.  A large
   number of the reactions cleanly destroy both gliders leaving nothing.
   Many of the remaining reactions cleanly create some common objects,
   and so are used as the first steps in {glider synthesis} or as part
   of constructing interesting objects using {rake}s.  Only a small
   number of collisions can be considered {dirty} due to creating
   multiple objects or a mess.
     Here is a list of the possible results along with how many
   different ways they can occur (ignoring reflections and rotations).
   -------------------------------
   result     right-angle  head-on
   -------------------------------
   nothing             11       17
   {beehive}            1        0
   {B-heptomino}        1        2
   {bi-block}           1        0
   {blinker}            2        1
   {block}              3        3
   {boat}               0        1
   {eater1}             1        0
   {glider}             1        1
   {honey farm}         3        2
   {interchange}        1        0
   {loaf}               0        1
   {lumps of muck}      1        0
   {octomino}           0        1
   {pi-heptomino}       2        1
   {pond}               1        1
   {teardrop}           1        0
   {traffic light}      2        1
   {four skewed blocks} 0        1
   {dirty}              6        0
   -------------------------------
   The messiest of the two-glider collisions in the "dirty" category is
   {2-glider mess}.

:2-glider mess:  A constellation made up of eight {blinker}s, four
   {block}s, a {beehive} and a {ship}, plus four emitted {glider}s,
   created by the following {2-glider collision}.
	..*.........
	*.*.........
	.**.........
	...........*
	.........**.
	..........**
   Two of the blocks, two of the gliders, and the ship are the standard
   signature {ash} of a {Herschel}.

:30P5H2V0: (2c/5 orthogonally, p5)  A spaceship discovered by Paul Tooke
   on 7 December 2000.  With just 30 cells, it is currently the smallest
   known 2c/5 spaceship.  A {glider synthesis} for 30P5H2V0 was found by
   Martin Grant in January 2015, based on a predecessor by Tanner
   Jacobi.
	....*........
	...***.......
	..**.**......
	.............
	.*.*.*.*..*..
	**...*...***.
	**...*......*
	..........*.*
	........*.*..
	.........*..*
	............*

:31c/240:  The rate of travel of the {31c/240 Herschel-pair climber}
   reaction, and {Caterpillar}-type spaceships based on that reaction.
   Each {Herschel} travels 31 cells orthogonally every 240 {tick}s.

:31c/240 Herschel-pair climber:  The mechanism defining the rate of
   travel of the {Centipede} and {shield bug} spaceships.  Compare
   {pi climber}.  It consists of a pair of {Herschel}s climbing two
   parallel chains of blocks.  Certain spacings between the block chains
   allow gliders from each Herschel to delete the extra ash objects
   produced by the other Herschel.  Two more gliders escape, one to each
   side, leaving only an exact copy of the original block chains, but
   shifted forward by 9 cells:
	**.........................................................**
	**.........................................................**
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	**.........................................................**
	**.........................................................**
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.............................................................
	.......................................................***...
	.......................................................*..*..
	.......................................................*..*..
	......................................................****...
	.......***............................................**.....
	........*............................................*.......
	......***.............................................*......
	......................................................*......

:3c/7 spaceship:  A {spaceship} travelling at three sevenths of the
   {speed of light}.  The only such spaceships that are currently known
   travel orthogonally.  The first to be found was the
   {spaghetti monster}, found by Tim Coe in June 2016.

:3-engine Cordership:  See {Cordership}.

:44P5H2V0: (2c/5 orthogonally, p5)  A {spaceship} discovered by Dean
   Hickerson on 23 July 1991, the first 2c/5 spaceship to be found.
   Small {tagalong}s were found by Robert Wainwright and David Bell that
   allowed the creation of arbitrarily large 2c/5 spaceships. These were
   the only known 2c/5 spaceships until the discovery of {70P5H2V0} in
   December 1992.
	....*.....*....
	...***...***...
	..*..*...*..*..
	.***.......***.
	..*.*.....*.*..
	....**...**....
	*....*...*....*
	.....*...*.....
	**...*...*...**
	..*..*...*..*..
	....*.....*....

:45-degree LWSS-to-G:  = {45-degree MWSS-to-G}.

:45-degree MWSS-to-G:  The following small {converter}, which accepts an
   MWSS or LWSS as input and produces an output glider travelling at a
   45-degree angle relative to the input direction.
	.........*.**....*.....
	.........**.*...*.*....
	................*.*....
	.......*****...**.***..
	......*..*..*........*.
	......**...**..**.***..
	...............**.*....
	......................*
	....................***
	...................*...
	...................**..
	.*****.................
	*....*.................
	.....*.................
	*...*..................
	..*.............**.....
	...............*..*....
	................**.....
	........**.............
	.......*.*.............
	.......*...............
	......**...............
	...................**..
	...................*...
	....................***
	......................*

:4-8-12 diamond:  The following {pure glider generator}.
	....****....
	............
	..********..
	............
	************
	............
	..********..
	............
	....****....

:4 boats: (p2)
	...*....
	..*.*...
	.*.**...
	*.*..**.
	.**..*.*
	...**.*.
	...*.*..
	....*...

:4F:  = {Fast Forward Force Field}.  This term is no longer in common
   use.

:4g-to-5g reaction:  A reaction involving 4 gliders which cleanly
   produces 5 gliders.  The one shown below was found by Dieter Leithner
   in July 1992:
	*.*..........................................
	.**..........................................
	.*...........................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.................*...........................
	...............*.*..*........................
	................**..*.*....................*.
	....................**....................**.
	..........................................*.*
     The first two gliders collide to produce a {traffic light} and
   glider.  The other two gliders react symmetrically with the evolving
   {traffic light} to form four gliders.  A {glider gun} can be built by
   using {reflector}s to turn four of the output gliders so that they
   repeat the reaction.

:56P6H1V0: (c/6 orthogonally, p6)  A 56-cell {spaceship} discovered by
   Hartmut Holzwart in 2009, the smallest known c/6 orthogonal spaceship
   as of July 2018.
	.....***..........***.....
	***.*.......**.......*.***
	....*...*..*..*..*...*....
	....*.....*....*.....*....
	..........**..**..........
	.......*...*..*...*.......
	.......*.*......*.*.......
	........**********........
	..........*....*..........
	........*........*........
	.......*..........*.......
	........*........*........

:58P5H1V1: (c/5 diagonally, p5)  A {spaceship} discovered by Matthias
   Merzenich on 5 September 2010. In terms of its minimum population of
   58 cells it is the smallest known c/5 diagonal spaceship. It provides
   sparks at its trailing edge which can perturb gliders, and this
   property was used to create the first c/5 diagonal puffers. These
   sparks also allow the attachment of tagalongs which was used to
   create the first c/5 diagonal wickstretcher in January 2011.
	....................**.
	....................**.
	...................*..*
	................**.*..*
	......................*
	..............**...*..*
	..............**.....*.
	...............*.*****.
	................*......
	.......................
	.......................
	.............***.......
	.............*.........
	...........**..........
	.....**....*...........
	.....***...*...........
	...*....*..............
	...*...*...............
	.......*...............
	..**.*.*...............
	**.....*...............
	**....**...............
	..****.................

:5c/9 wire:  A {wire} discovered by Dean Hickerson in April 1997, using
   his {dr} {search program}.  It supports {signal}s that travel through
   the wire diagonally at five ninths of the {speed of light}.  See also
   {2c/3 wire}.
	....*.**............................................
	....**..*...........................................
	.......*..*.........................................
	..*****.**.*..*.....................................
	.*..*...*..****.....................................
	.*.**.*.*.*......*..................................
	**.*.****.*..*****..................................
	...*......*.*.....**................................
	**.*.****.*..*.**.*.*...............................
	*..*.*..*.**.*.*.*..*...............................
	..**..*..*...*.*....*.**............................
	....**....****.**..**..*............................
	....*...*.*......*...*..............................
	.....****.*.*****.***...*...........................
	.........*.*....*.*..****...........................
	.......*...*..*...*.*......*........................
	.......**..*.*.****.*..*****........................
	..........**.*......*.*.....**......................
	.............*.****.*..*.**.*.*.....................
	.............*.*..*.**.*.*.*..*.....................
	............**..*..*...*.*....*.**..................
	..............**....****.**..**..*..................
	..............*...*.*......*...*....................
	...............****.*.*****.***...*.................
	...................*.*....*.*..****.................
	.................*...*..*...*.*......*..............
	.................**..*.*.****.*..*****..............
	....................**.*......*.*.....**............
	.......................*.****.*..*.**.*.*...........
	.......................*.*..*.**.*.*.*..*...........
	......................**..*..*...*.*....*.**........
	........................**....****.**..**..*........
	........................*...*.*......*...*..........
	.........................****.*.*****.***...*.......
	.............................*.*....*.*..****.......
	...........................*...*..*...*.*......*....
	...........................**..*.*.****.*..*****....
	..............................**.*......*.*.....**..
	.................................*.****.*..*.**.*..*
	.................................*.*..*.**.*.*.*..**
	................................**..*..*...*.*......
	..................................**....****.**.....
	..................................*...*.*......*....
	...................................****.*.*****.*...
	.......................................*.*....*.*...
	.....................................*...*..*...**..
	.....................................**..*.*.***..*.
	........................................**.*.....*..
	............................................*.***...
	.............................................**.....

:60P312: (p312) Found by Dave Greene, 1 November 2004, based on
   {92P156}.
	....................**....................
	....................**....................
	..........................................
	..........................................
	..........................................
	...............................**.........
	......................**......*..*........
	......................*........**.........
	......*...............*...................
	.....*.*...............*..................
	.....*.*..................................
	......*...................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	................................*..*......
	.................................***......
	**......................................**
	**......................................**
	......***.................................
	......*..*................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	...................................*......
	..................................*.*.....
	..................*...............*.*.....
	...................*...............*......
	.........**........*......................
	........*..*......**......................
	.........**...............................
	..........................................
	..........................................
	..........................................
	....................**....................
	....................**....................

:60P5H2V0: (2c/5 orthogonally, p5)  A 60-cell {spaceship} discovered by
   Tim Coe in May 1996.  It was the first non-c/2 orthogonal spaceship
   to be successfully constructed via {glider synthesis}.
	.....*.......*.....
	...**.**...**.**...
	......**...**......
	........*.*........
	.*....*.*.*.*....*.
	***.....*.*.....***
	*.....*.*.*.*.....*
	..*..*..*.*..*..*..
	..**...**.**...**..
	*.......*.*.......*
	*......**.**......*

:67P5H1V1: (c/5 diagonally, p5)  A {spaceship} discovered by Nicolay
   Beluchenko in July 2006. It was the smallest known c/5 diagonal
   spaceship until the discovery of {58P5H1V1} in September 2010.
	.....***..............
	....*...**............
	...**...*.............
	..*.....*.............
	.*.**....**...........
	**..*......*..........
	...**..*..............
	...**.**..............
	....*.................
	.....*****............
	......*..***..**......
	.........*.**..*.**...
	.........*...*.*..*...
	..........*****.....*.
	.........*..*..*.....*
	.....................*
	................***...
	................*.....
	...............*......
	................**....

:70P5H2V0: (2c/5 orthogonally, p5)  A {spaceship} discovered by Hartmut
   Holzwart on 5 December 1992.
	..*............*..
	.*.*..........*.*.
	**.**........**.**
	**..............**
	..*............*..
	..****......****..
	..*..**....**..*..
	...**..*..*..**...
	....**.****.**....
	.....*.*..*.*.....
	......*....*......
	..................
	.....*......*.....
	...**.**..**.**...
	....*........*....
	....**......**....

:7x9 eater:  A high-{clearance} {eater5} variant that can suppress
   passing gliders in tight spaces, such as on the inside corner of an
   {R64} {Herschel conduit}.  Like the eater5 and {sidesnagger}, the 7x9
   eater is able to eat gliders coming from two directions, though this
   ability is not commonly used.
	.*..........
	..*.........
	***.........
	............
	......*.....
	.....*......
	.....***....
	............
	............
	......*...**
	.....*.*...*
	.....**...*.
	.........*..
	.....*****.*
	.....*....**
	......***...
	........*.**
	.........*.*

:83P7H1V1:  = {lobster}

:86P5H1V1: (c/5 diagonally, p5)  A {spaceship} discovered by Jason
   Summers on January 8, 2005.  It was the smallest known c/5 diagonal
   spaceship until the discovery of {67P5H1V1} in July 2006.
	.........***...........
	........*..............
	.......*...............
	...........**..........
	........**.*...........
	..............***......
	...........*..**..**...
	..*........**.*...**...
	.*..*......*..**.......
	*...*..................
	*...........*..*.......
	*..**.***...*...**.**..
	...*...*..**..*..*.....
	.................**..*.
	.....****...*.....*...*
	.....**.*.*..........*.
	.....*.....*......**...
	...........***.........
	......**.....**.*......
	......**...*....*......
	...........*...........
	.............*.*.......
	..............*........

:90-degree kickback:  See {kickback reaction}.

:92P156: (p156) Discovered by Jason Summers on October 31, 2004.  It is
   actually an eight-barrel {glider gun}, with all output gliders
   suppressed by {eater1}s. Replacing each pair of eater1s with a
   {beehive} doubles the period and produces {60P312}.
	....................**....................
	....................**....................
	..........................................
	..........................................
	..........................................
	........**......................**........
	.........*............**........*.........
	.........*.*..........*.......*.*.........
	.....*....**..........*.......**....*.....
	.....***...............*..........***.....
	........*........................*........
	.......**........................**.......
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	................................*..*......
	.................................***......
	**......................................**
	**......................................**
	......***.................................
	......*..*................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	.......**........................**.......
	........*........................*........
	.....***..........*...............***.....
	.....*....**.......*..........**....*.....
	.........*.*.......*..........*.*.........
	.........*........**............*.........
	........**......................**........
	..........................................
	..........................................
	..........................................
	....................**....................
	....................**....................

:9hd:  Separated by 9 {half diagonal}s.  Specifically used to describe
   the distance between the two {construction lane}s in the
   {linear propagator}.

:Achim's p144: (p144)  This was found (minus the blocks shown below) on
   a cylinder of width 22 by Achim Flammenkamp in July 1994.  Dean
   Hickerson reduced it to a finite form using {figure-8}s the same day.
   The neater finite form shown here, replacing the figure-8s with
   blocks, was found by David Bell in August 1994.  See {factory} for a
   use of this oscillator.
	**........................**
	**........................**
	..................**........
	.................*..*.......
	..................**........
	..............*.............
	.............*.*............
	............*...*...........
	............*..*............
	............................
	............*..*............
	...........*...*............
	............*.*.............
	.............*..............
	........**..................
	.......*..*.................
	........**..................
	**........................**
	**........................**

:Achim's p16: (p16)  Found by Achim Flammenkamp, July 1994.
	.......**....
	.......*.*...
	..*....*.**..
	.**.....*....
	*..*.........
	***..........
	.............
	..........***
	.........*..*
	....*.....**.
	..**.*....*..
	...*.*.......
	....**.......

:Achim's p4: (p4)  Dave Buckingham found this in a less compact form
   (using two halves of {sombreros}) in 1976.  The form shown here was
   found by Achim Flammenkamp in 1988.  The {rotor} is two copies of the
   rotor of {1-2-3-4}, so the oscillator is sometimes called the "dual
   1-2-3-4".
	..**...**..
	.*..*.*..*.
	.*.**.**.*.
	**.......**
	..*.*.*.*..
	**.......**
	.*.**.**.*.
	.*..*.*..*.
	..**...**..

:Achim's p5:  = {pseudo-barberpole}

:Achim's p8: (p8)  Found by Achim Flammenkamp, July 1994.
	.**......
	*........
	.*...*...
	.*...**..
	...*.*...
	..**...*.
	...*...*.
	........*
	......**.

:acorn: (stabilizes at time 5206)  A {methuselah} found by Charles
   Corderman.  It has a final population of 633 and covers an area of
   215 by 168 cells, not counting the 13 gliders it produces.  Its {ash}
   consists of typical stable objects and blinkers, along with the
   relatively rare {mango} and a temporary {eater1}.
	.*.....
	...*...
	**..***

:A for all: (p6)  Found by Dean Hickerson in March 1993.
	....**....
	...*..*...
	...****...
	.*.*..*.*.
	*........*
	*........*
	.*.*..*.*.
	...****...
	...*..*...
	....**....

:against the grain:  A term used for {negative spaceship}s travelling in
   {zebra stripes} agar, perpendicular to the stripes, and also for
   {against-the-grain grey ship}s.
     Below is a sample {signal}, found by Hartmut Holzwart in April
   2006, that travels against the grain at {2c/3}.  This "negative
   spaceship" travels upward and will quickly reach the edge of the
   finite patch of stabilized agar shown here.
	...*..*..*..*..*..*..*..*..*..*..*...
	.***********************************.
	*...................................*
	.***********************************.
	.....................................
	.***********************************.
	*...................................*
	.***********************************.
	.....................................
	.***********************************.
	*...................................*
	.***********************************.
	.....................................
	.***********************************.
	*...................................*
	.*****************..****************.
	.....................................
	.***************......**************.
	*...............*....*..............*
	.****************....***************.
	.....................................
	.*************...****...************.
	*.................**................*
	.************............***********.
	.............*..........*............
	.**************........*************.
	*..............*......*.............*
	.***************......**************.
	..........**....*....*....**.........
	.*******......****..****......******.
	*.......*...**...*..*...**...*......*
	.*******.........*..*.........******.
	.........*.....*......*.....*........
	.*********......*....*......********.
	*.........*....**.**.**....*........*
	.***********....*....*....**********.
	............**....**....**...........
	.*******..***.*..*..*..*.***..******.
	*..............***..***.............*
	.*****......***.*....*.***......****.
	......*....*..............*....*.....
	.******........*......*........*****.
	*......*...**..*..**..*..**...*.....*
	.********.....*.**..**.*.....*******.
	.........*..*.**......**.*..*........
	.*********...**........**...********.
	*..........*..............*.........*
	.****************....***************.
	.................****................
	.*****************..****************.
	*...................................*
	.***********************************.
	...*..*..*..*..*..*..*..*..*..*..*...
     Holzwart proved in 2006 that 2c/3 is the maximum speed at which
   signals can move non-destructively against the grain through zebra
   stripes agar.

:against-the-grain grey ship:  A {grey ship} in which the region of
   density 1/2 consists of lines of ON cells lying perpendicular to the
   direction in which the spaceship moves.  See also
   {with-the-grain grey ship}.

:agar:  Any pattern covering the whole plane that is periodic in both
   space and time.  The simplest (nonempty) agar is the {stable} one
   extended by the known {spacefiller}s.  For some more examples see
   {chicken wire}, {houndstooth agar}, {onion rings}, {squaredance} and
   {Venetian blinds}.  Tiling the plane with the pattern O......O
   produces another interesting example: a p6 agar which has a phase of
   {density} 3/4, which is the highest yet obtained for any phase of an
   oscillating pattern.  See {lone dot agar} for an agar composed of
   isolated cells.

:aircraft carrier: (p1)  This is the smallest {still life} that has more
   than one {island}.
	**..
	*..*
	..**

:airforce: (p7)  Found by Dave Buckingham in 1972.  The rotor consists
   of two copies of that used in the {burloaferimeter}.
	.......*......
	......*.*.....
	.......*......
	..............
	.....*****....
	....*.....*.**
	...*.**...*.**
	...*.*..*.*...
	**.*...**.*...
	**.*.....*....
	....*****.....
	..............
	......*.......
	.....*.*......
	......*.......

:AK47 reaction:  The following reaction (found by Rich Schroeppel and
   Dave Buckingham) in which a honey farm predecessor, catalysed by an
   eater and a block, reappears at another location 47 generations
   later, having produced a glider and a traffic light.  This was in
   1990 the basis for the Dean Hickerson's construction of the first
   {true} p94 gun,  and for a very small (but {pseudo}) p94 glider gun
   found by Paul Callahan in July 1994.  (The original true p94 gun was
   enormous, and has now been superseded by comparatively small
   {Herschel loop} guns and Mike Playle's tiny {AK94 gun}.)
	.....*....
	....*.*...
	...*...*..
	...*...*..
	...*...*..
	....*.*...
	.....*....
	..........
	..**......
	...*......
	***.....**
	*.......**

:AK94 gun:  The smallest known gun using the {AK47 reaction}, found by
   Mike Playle in May 2013 using his {Bellman} program.
	.......*.......*.......**.............
	.......***.....***.....**.............
	..........*.......*...................
	.........**......**................**.
	..............................**..*..*
	..............................*.*..**.
	.................................**...
	.....*............................*...
	.....***..........................*.**
	........*......................**.*..*
	.......**......................**.**..
	......................................
	......................................
	.................*....................
	..**.**.........*.*..........**.......
	*..*.**........*...*.........*........
	**.*...........*...*..........***.....
	...*...........*...*............*.....
	...**...........*.*...................
	.**..*.*.........*....................
	*..*..**..............................
	.**................**.................
	...................*..................
	.............**.....***...............
	.............**.......*...............

:Al Jolson:  = {Jolson}

:almost knightship:  A promising {partial result} discovered by Eugene
   Langvagen in March 2004.  This was an early near miss in the ongoing
   search for a small {elementary} (2,1)c/6 {knightship}. After six
   generations, only two cells are incorrect.
	....***......
	...**..**....
	..*..***.**..
	.***.........
	...**....**..
	**.*.........
	**..***......
	....**.*.....
	**.***.......
	.*...*.**....
	.....*.**....
	*...*....*...
	*...*..***.**
	*............
	.*.*..*......
	.....*.....**
	......*.**...
	......**..*..
	...........*.

:almosymmetric: (p2)  Found in 1971.
	....*....
	**..*.*..
	*.*......
	.......**
	.*.......
	*......*.
	**.*.*...
	.....*...

:ambidextrous:  A type of {Herschel transceiver} where the {receiver}
   can be used in either of two mirror-image orientations.  See also
   {chirality}.

:anteater:  A pattern that consumes {ants}.  Matthias Merzenich
   discovered a c/5 anteater on 15 April 2011.  See {wavestretcher} for
   details.

:antlers:  = {moose antlers}

:ants: (p5 wick)  The standard form is shown below.  It is also possible
   for any ant to be displaced by one or two cells relative to either or
   both of its neighbouring ants.  Dean Hickerson found {fencepost}s for
   both ends of this wick in October 1992 and February 1993.  See
   {electric fence}, and also {wickstretcher}.
	**...**...**...**...**...**...**...**...**..
	..**...**...**...**...**...**...**...**...**
	..**...**...**...**...**...**...**...**...**
	**...**...**...**...**...**...**...**...**..

:antstretcher:  Any {wickstretcher} or {wavestretcher} that stretches
   {ants}.  Nicolay Beluchenko and Hartmut Holzwart constructed the
   following small {extensible} antstretcher in January 2006:
	......................................................**.......
	.....................................................**........
	...............................................**.....*........
	..............................................**.....**........
	................................................*....*.*..**...
	..................................................**...**.****.
	..................................................**..........*
	..............................................................*
	........................................................*......
	..........................................................**...
	...............................................................
	..........................................................***..
	.........................................................**..*.
	...............................**..........................*...
	..............................**...............................
	...............................*.*...................***..*....
	..........................*....***...................*..***....
	.........................*****.***..*.**................**.....
	.........................*..**......*...**.**.........**.**....
	...................................*....**...**.**.......**....
	...........................**..**.**..**.....**...**.*.*.......
	...................................*.......**.....**...........
	.....................***...*.....**.............**....*........
	.....................*.....*..*.**...................*.........
	......................*...**.*.................................
	.........................**...*.*..............................
	.............***..........*....................................
	.............*.....***..**.....................................
	..............*..**.***.**.....................................
	................*..........*...................................
	.................*.*.**....*...................................
	...................**.*........................................
	.................**...*.*......................................
	................**.............................................
	..................*............................................
	...............**..............................................
	..............***..............................................
	.............**.*..............................................
	............****.*.............................................
	.................***...........................................
	..................**...........................................
	..........***.**...............................................
	.........*...***...............................................
	............***................................................
	........*.*.*..................................................
	.......****....................................................
	.......*.......................................................
	........**.....................................................
	.........*..*..................................................
	**.............................................................
	*.*...***......................................................
	*...*....*.....................................................
	...**..........................................................
	...*.....*.....................................................

:anvil:  The following {induction coil}.
	.****..
	*....*.
	.***.*.
	...*.**

:apgluxe:  See {apgsearch}

:apgmera:  See {apgsearch}.

:apgnano:  See {apgsearch}.

:apgsearch:  One of several versions of a client-side Ash Pattern
   Generator {soup} search script by Adam P. Goucher, for use with
   Conway's Life and a wide variety of other rules. Development of the
   original {Golly}-based Python script started in August 2014.  After
   the addition in 2016 of apgnano (native C++) and apgmera
   (self-modifying, 256-bit SIMD compatibility), development continues
   in 2017 with apgluxe (Larger Than Life and Generations rules, more
   soup shapes).  Several customized variants of the Python script have
   also been created by other programmers, to perform types of searches
   not supported by Goucher's original apgsearch 1.x.
     All of these versions of the search utility work with a "haul" that
   usually consists of many thousands or millions of random soup
   patterns.  Each soup is run to stability, and detailed object
   {census} results are reported to {Catagolue}.  For any rare objects
   discovered in the {ash}, the source soup can be easily retrieved from
   the Catagolue server.

:APPS: (c/5 orthogonally, p30)  An asymmetric {PPS}.  The same as the
   {SPPS}, but with the two halves 15 generations out of phase with one
   another.  Found by Alan Hensel in May 1998.

:ark:  A pair of mutually stabilizing {switch engine}s.  The archetype
   is {Noah's ark}.  The diagram below shows an ark found by Nick Gotts
   that takes until generation 736692 to stabilize, and can therefore be
   considered as a {methuselah}.
	...........................*....
	............................*...
	.............................*..
	............................*...
	...........................*....
	.............................***
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	**..............................
	..*.............................
	..*.............................
	...****.........................

:arm:  A long extension, sometimes also called a "wing", hanging off
   from the main body of a {spaceship} or {puffer} perpendicular to the
   direction of travel.  For example, here is a sparking c/3 spaceship
   which contains two arms.
	............***............
	...........*...............
	..........**...............
	....*.**..**..***..........
	...**.**.**.....*....**....
	..*..**...*.**....**.**....
	........****......**...*...
	....*.*.**........**.......
	......*....................
	...**......................
	..**..*....................
	....***.**.................
	*..*.....***...............
	.*.****.*...*..............
	........**....*......*.....
	.........*....**....**.***.
	........*...*..**..**.....*
	..........*..*.*..*.....**.
	...........*.***....*......
	............***..***.*.....
	...........**...***........
	..................*..*.....
	...................*.......
   Many known spaceships have multiple arms, usually fairly narrow.
   This is an artefact of the search methods used to find such
   spaceships, rather than an indication of what a "typical" spaceship
   might look like.
     For an alternate meaning see {construction arm}.

:armless:  A method of generating {slow salvo}s across a wide range of
   lanes without using a {construction arm} with a movable {elbow}.
   Instead, streams of gliders on two fixed opposing {lane}s collide
   with each other to produce clean 90-degree output gliders.  Slowing
   down one of the streams by 8N ticks will move the output lanes of the
   gliders toward the source of that stream by N {full diagonal}s.  This
   construction method was used to create the supporting slow salvos in
   the {half-baked knightship}s, and also in the {Parallel HBK gun}.

:ash:  The {stable} or oscillating objects left behind when a chaotic
   reaction stabilizes, or "burns out". Experiments show that for random
   {soup}s with moderate initial densities (say 0.25 to 0.5) the
   resulting ash has a density of about 0.0287.  (This is, of course,
   based on what happens in finite fields. In infinite fields the
   situation may conceivably be different in the long run because of the
   effect of certain initially very rare objects such as {replicator}s.)

:asynchronous:  Indicates that precise relative timing is not needed for
   two or more input {signal}s entering a {circuit}, or two or more sets
   of {glider}s participating in a {glider synthesis}.  In some cases
   the signals or sets of gliders can arrive in any order at all - i.e.,
   they have non-overlapping effects.
     However, in some cases such as {slow salvo} constructions, there is
   a required order for some of the incoming signals.  These signals can
   still be referred to as "asynchronous" because the number of ticks
   between them is infinitely adjustable:  arbitrarily long delays can
   be added with no change to the final result.  Compare {synchronized}.

:aVerage: (p5)  Found by Dave Buckingham, 1973.  The average number of
   live {rotor} cells is five (V), which is also the period.
	...**........
	....***......
	..*....*.....
	.*.****.*....
	.*.*....*..*.
	**.***..*.*.*
	.*.*....*..*.
	.*.****.*....
	..*....*.....
	....***......
	...**........

:B:  = {B-heptomino}

:B29: (c/4 diagonally, p4)  The following {spaceship}, found by Hartmut
   Holzwart in April 2004.  A glider synthesis of this spaceship was
   completed by Tanner Jacobi in April 2015.
	.......***.......
	.......*.........
	***......*.......
	*......*.*.......
	.*....**.****....
	...****.*****.**.
	....**.......**.*

:B-52 bomber:  The following p104 {double-barrelled} {glider} {gun}. It
   uses a {B-heptomino} and emits one glider every 52 generations. It
   was found by Noam Elkies in March 1996, except that Elkies used
   {blocker}s instead of {mold}s, the improvement being found by David
   Bell later the same month.
	.**....................................
	.**.................*..................
	...................*.*............*.*..
	....................*............*.....
	**.......**.......................*..*.
	**.*.....**.......................*.*.*
	...*.......................*.......*..*
	...*.......................**.......**.
	*..*.................**.....*..........
	.**..................*.................
	.....................***...............
	....................................**.
	....................................**.
	.**....................................
	*..*...................................
	*.*.*................*.*....**.....**..
	.*..*.................**....**.....**.*
	.....*............*...*...............*
	..*.*............*.*..................*
	..................*................*..*
	....................................**.

:B60:  A {Herschel conduit} discovered by Michael Simkin in 2015 using
   his search program, {CatForce}.  It is one of two known {Blockic}
   {elementary conduit}s.  After 60 ticks, it produces a Herschel
   rotated 180 degrees at (-6,-10) relative to the input.  It can most
   easily be connected to another B60 conduit, producing a closed loop,
   the {Simkin glider gun}.
	*...........**.....**
	***.........**.....**
	..*..................
	..*............**....
	...............**....
	.....................
	.....................
	.....................
	.....................
	......*..............
	......*.*............
	......***............
	........*............

:babbling brook:  Any {oscillator} whose {rotor} consists of a string of
   cells each of which is adjacent to exactly two other rotor cells,
   except for the endpoints which are adjacent to only one other rotor
   cell.  Compare {muttering moat}.  Examples include the {beacon}, the
   {great on-off}, the {light bulb} and the {spark coil}.  The following
   less trivial example (by Dean Hickerson, August 1997) is the only one
   known with more than four cells in its rotor.  It is p4 and has a
   6-cell rotor.
	.......*........
	.....***....**..
	....*...**..*...
	.*..*.**..*.*...
	*.*.*....**..**.
	.**..**....*.*.*
	...*.*..**.*..*.
	...*..**...*....
	..**....***.....
	........*.......

:backrake:  Another term for a backwards {rake}.  A p8 example by Jason
   Summers is shown below.  See {total aperiodic} for a p12 example.
	.....***...........***.....
	....*...*.........*...*....
	...**....*.......*....**...
	..*.*.**.**.....**.**.*.*..
	.**.*....*.**.**.*....*.**.
	*....*...*..*.*..*...*....*
	............*.*............
	**.......**.*.*.**.......**
	............*.*............
	......***.........***......
	......*...*.........*......
	......*.*....***...........
	............*..*....**.....
	...............*...........
	...........*...*...........
	...........*...*...........
	...............*...........
	............*.*............

:backward glider:  A {glider} which moves at least partly in the
   opposite direction to the {puffer}(s) or {spaceship}(s) under
   consideration.

:bait:  An object in a {converter}, usually a small {still life}, that
   is temporarily destroyed by an incoming {signal}, but in such a way
   that a usable output signal is produced.  In general such a converter
   produces multiple output signals (or a signal {splitter} is added)
   and one branch of the output is routed to a {factory} mechanism that
   rebuilds the bait object so that the converter can be re-used.

:baker: (c p4 fuse)  A {fuse} by Keith McClelland.
	..............**
	.............*.*
	............*...
	...........*....
	..........*.....
	.........*......
	........*.......
	.......*........
	......*.........
	.....*..........
	....*...........
	...*............
	***.............
	.*..............

:baker's dozen: (p12)  A {loaf} {hassle}d by two {block}s and two
   {caterer}s.  The original form (using p4 and p6 oscillators to do the
   hassling) was found by Robert Wainwright in August 1989.
	**.........**..........
	****.*.....**..........
	*.*..***...............
	...........*...........
	....**....*.*..........
	....*.....*..*....*....
	...........**....**....
	.......................
	...............***..*.*
	..........**.....*.****
	..........**.........**

:bakery: (p1)  A common formation of two bi-loaves.
	....**....
	...*..*...
	...*.*....
	.**.*...*.
	*..*...*.*
	*.*...*..*
	.*...*.**.
	....*.*...
	...*..*...
	....**....

:banana spark:  A common three-bit {polyplet} spark used in
   {glider synthesis} and {signal} {circuit}ry.  The {buckaroo} is an
   {oscillator} that produces this spark.  It can be used to turn a
   glider 90 degrees:
	..*....
	*.*....
	.**....
	....**.
	......*

:barberpole:  Any p2 oscillator in the infinite sequence {bipole},
   {tripole}, {quadpole}, {pentapole}, {hexapole}, {heptapole} ... (It
   wasn't my idea to suddenly change from Latin to Greek.) This sequence
   of oscillators was found by the MIT group in 1970. The term is also
   used (usually in the form "barber pole") to describe other
   {extensible} sections of oscillators or spaceships, especially those
   (usually of period 2) in which all generations look alike except for
   a translation and/or rotation/reflection.  Any barberpole can be
   lengthened by the reaction shown in {barbershop}.  See also
   {pseudo-barberpole}.

:barberpole intersection:  = {quad}

:barbershop:  An object created by Jason Summers in 1999 which builds an
   infinite {barberpole}.  It uses {slide gun}s to repeatedly lengthen a
   {barberpole} at a speed of c/124.  The key lengthening reaction from
   Mark Niemiec is shown below:
	..........*.*.......
	...........**.......
	.*.........*.....*..
	..*..............*.*
	***..............**.
	....................
	....................
	....................
	.................*..
	................**..
	................*.*.
	........**..........
	.......*.*..........
	....................
	.....*.*............
	.....**.............

:barber's pole:  = {barberpole}

:barge: (p1)
	.*..
	*.*.
	.*.*
	..*.

:basic shuttle:  = {queen bee shuttle}

:beacon: (p2)  The third most common {oscillator}.  Found by Conway,
   March 1970.
	**..
	*...
	...*
	..**

:beacon maker: (c p8 fuse)
	..............**
	.............*.*
	............*...
	...........*....
	..........*.....
	.........*......
	........*.......
	.......*........
	......*.........
	.....*..........
	....*...........
	...*............
	***.............
	..*.............
	..*.............

:beehive: (p1)  The second most common {still life}.
	.**.
	*..*
	.**.

:beehive and dock: (p1)
	...**.
	..*..*
	...**.
	......
	.****.
	*....*
	**..**

:beehive on big table:  = {beehive and dock}

:beehive pusher:  = {hivenudger}

:beehive stopper:   A {Spartan} logic circuit discovered by Tanner
   Jacobi on 12 May 2015.  It converts an input {glider} {signal} into a
   {beehive}, in such a way that the beehive can cleanly absorb a single
   glider from a perpendicular glider {stream}.  The circuit can't be
   re-used until the beehive "bit" is cleared by the passage of at least
   one perpendicular input.
	.*..........................
	..*.........................
	***.........................
	............................
	............................
	................*...........
	...............*............
	...............***..........
	............................
	............*...............
	............*.*.............
	............**..............
	...**.....*.................
	...**....*.*................
	.........*.*................
	..........*.................
	........................**..
	........................*.*.
	..........................*.
	...............**.........**
	........**.....**...........
	.......*.*..................
	.......**...................
	............................
	..........**................
	..........*.................
	...........***..............
	.............*..............
     This term has sometimes been used for the beehive {catalyst}
   variant of {SW-2}, and also for Paul Callahan's larger
   {glider stopper}, which also provides optional 0-degree and
   180-degree glider outputs.

:beehive wire:  See {lightspeed wire}.

:beehive with tail: (p1)
	.**...
	*..*..
	.**.*.
	....*.
	....**

:Bellman:  A program for searching catalytic reactions, developed by
   Mike Playle, which successfully found the {Snark}.

:belly spark:  The spark of a {MWSS} or {HWSS} other than the
   {tail spark}.

:Beluchenko's p37: (p37)  Found by Nicolay Beluchenko on April 14, 2009.
   It was the first {period} 37 {oscillator} to be found, and remains
   the smallest.
	...........**...........**...........
	...........**...........**...........
	.....................................
	.....................................
	......*.......................*......
	.....*.*.....*.........*.....*.*.....
	....*..*.....*.**...**.*.....*..*....
	.....**..........*.*..........**.....
	...............*.*.*.*...............
	................*...*................
	.....................................
	**.................................**
	**.................................**
	.....**.......................**.....
	.....................................
	......*.*...................*.*......
	......*..*.................*..*......
	.......**...................**.......
	.....................................
	.......**...................**.......
	......*..*.................*..*......
	......*.*...................*.*......
	.....................................
	.....**.......................**.....
	**.................................**
	**.................................**
	.....................................
	................*...*................
	...............*.*.*.*...............
	.....**..........*.*..........**.....
	....*..*.....*.**...**.*.....*..*....
	.....*.*.....*.........*.....*.*.....
	......*.......................*......
	.....................................
	.....................................
	...........**...........**...........
	...........**...........**...........

:Beluchenko's p51: (p51)  Found by Nicolay Beluchenko on February 17,
   2009.  It was the first non-{trivial} {period} 51 {oscillator} to be
   found.
	...............**...**...............
	.....................................
	.....................................
	......**.....................**......
	......**.....................**......
	.....................................
	...**...........................**...
	...**.........**.....**.........**...
	.........***.**.......**.***.........
	........*.*...............*.*........
	........**.................**........
	........*...................*........
	.....................................
	........*...................*........
	.......**...................**.......
	*......*.....................*......*
	*...................................*
	.....................................
	.....................................
	.....................................
	*...................................*
	*......*.....................*......*
	.......**...................**.......
	........*...................*........
	.....................................
	........*...................*........
	........**.................**........
	........*.*...............*.*........
	.........***.**.......**.***.........
	...**.........**.....**.........**...
	...**...........................**...
	.....................................
	......**.....................**......
	......**.....................**......
	.....................................
	.....................................
	...............**...**...............

:bent keys: (p3)  Found by Dean Hickerson, August 1989.  See also
   {odd keys} and {short keys}.
	.*........*.
	*.*......*.*
	.*.**..**.*.
	....*..*....
	....*..*....

:BFx59H:  One of the earliest and most remarkable {converter}s,
   discovered by Dave Buckingham in July 1996.  In 59 generations it
   transforms a B-heptomino into a clean Herschel with very good
   clearance, allowing easy connections to other conduits.  It forms the
   final stage of many of the known {composite conduit}s, including the
   majority of the original sixteen {Herschel conduit}s.  Here a
   {ghost Herschel} marks the output location:
	.**.....................
	..*.....................
	.*......................
	.**.....................
	........................
	........................
	........................
	........................
	........................
	*...**...............*..
	**..**...............*..
	.**..................***
	.*.....................*
	*.......................

:B-heptomino: (stabilizes at time 148)  This is a very common
   {methuselah} that evolves into three {block}s, two {glider}s and a
   {ship} after 148 generations. Compare with {Herschel}, which appears
   at generation 20 of the B-heptomino's evolution. B-heptominoes
   acquired particular importance in 1996 due to Dave Buckingham's work
   on {B track}s.  See in particular
   {My Experience with B-heptominos in Oscillators}.
	*.**
	***.
	.*..
     This pattern often arises with the cell at top left shifted one
   space to the left, producing a seven-bit {polyplet} that shares the
   same eight-bit descendant but is not technically a heptomino at all.
   This alternate form is shown as the input for {elementary}
   {converter} patterns such as {BFx59H} and {BRx46B}. This is standard
   practice for elementary {conduit}s, since many of these conduits do
   in fact produce this alternate form as output.
     The B-heptomino is considered a failed {puffer} or failed
   {spaceship}, since on its own it travels at c/2 for only a short time
   before being affected by its own trailing debris.  However, it can be
   stabilized into a c/2 puffer or into a {clean} c/2 rake or spaceship.
   See, e.g., {ecologist}.

:B-heptomino shuttle:  = {twin bees shuttle}

:bi-block: (p1)  The smallest {pseudo still life}.
	**.**
	**.**

:bi-block fuse:  A {clean} {fuse} made by a row of {bi-block}s separated
   by 2 cell gaps.  The bi-block row {wick} is usually created by a
   {bi-block puffer}. The {burn}ing advances 8 cells every 12
   generations making its speed {2c/3}.
	**..**..**..**..**..**..**..**..**..**..**..**.
	**..**..**..**..**..**..**..**..**..**..**.*..*
	............................................**.
	**..**..**..**..**..**..**..**..**..**..**.....
	**..**..**..**..**..**..**..**..**..**..**.....

:bi-block puffer:  Any {puffer} whose output is {bi-block}s.  The term
   is particularly used for p8 c/2 puffers, in which case a
   {bi-block fuse} is created.  A bi-block puffer is easily made using
   two {backrake}s whose gliders impact symmetrically.  Jason Summers
   {weld}ed two backrakes to form a more compact puffer, as shown below.
	...........*.*............**..............................
	..........*..*..........*....*............................
	.........**.......*....*..................................
	........*......**.*....*.....*............................
	.......******..*.......******.............................
	....**.......*...****.....................................
	...*...***.*....*.........................................
	..*...*...**.*..**.*..*...................................
	..*.....**...*.....*......................................
	..***...****.*.......*.**.................................
	...........*.........*..*......*..........................
	..***......*.*.......*..*....*.*..........................
	.*.....*.....*........**......**.....*..**..**..**..**..**
	*...**.*...**.......................**..**..**..**..**..**
	*...*......***............................................
	*...**.*...**.......................**..**..**..**..**..**
	.*.....*.....*........**......**.....*..**..**..**..**..**
	..***......*.*.......*..*....*.*..........................
	...........*.........*..*......*..........................
	..***...****.*.......*.**.................................
	..*.....**...*.....*......................................
	..*...*...**.*..**.*..*...................................
	...*...***.*....*.........................................
	....**.......*...****.....................................
	.......******..*.......******.............................
	........*......**.*....*.....*............................
	.........**.......*....*..................................
	..........*..*..........*....*............................
	...........*.*............**..............................
   By periodically burning the {bi-block fuse} using perturbations by a
   following backrake and spaceships, c/2 rakes can be created for all
   periods that are a multiple of eight.

:bi-boat:  = {boat-tie}

:biclock:  The following {pure glider generator} consisting of two
   {clock}s.
	..*....
	**.....
	..**...
	.*...*.
	...**..
	.....**
	....*..

:big beacon:  = {figure-8}

:big fish:  = {HWSS}

:big glider: (c/4 diagonally, p4)  This was found by Dean Hickerson in
   December 1989 and was the first known diagonal {spaceship} other than
   the {glider}.
	...***............
	...*..***.........
	....*.*...........
	**.......*........
	*.*....*..*.......
	*........**.......
	.**...............
	.*..*.....*.**....
	.*.........**.*...
	...*.*......**..*.
	....**.*....**...*
	........*.......*.
	.......****...*.*.
	.......*.**...****
	........*...**.*..
	.............**...
	.........*.***....
	..........*..*....

:big S: (p1)
	....**.
	...*..*
	...*.**
	**.*...
	*..*...
	.**....

:big table:  = {dock}

:billiard table:  = {billiard table configuration}.

:billiard table configuration:  Any {oscillator} in which the {rotor} is
   enclosed within the {stator}.  Examples include {airforce},
   {cauldron}, {clock II}, {Hertz oscillator}, {negentropy}, {pinwheel},
   {pressure cooker} and {scrubber}.

:bi-loaf:  This term has been used in at least three different senses. A
   bi-loaf can be half a {bakery}:
	.*.....
	*.*....
	*..*...
	.**.*..
	...*.*.
	...*..*
	....**.
   or it can be the following much less common {still life}:
	..*....
	.*.*...
	*..*...
	.**.**.
	...*..*
	...*.*.
	....*..
   or the following {pure glider generator}:
	..*.
	.*.*
	*..*
	.**.
	*..*
	*.*.
	.*..

:bipole: (p2)  The {barberpole} of length 2.
	**...
	*.*..
	.....
	..*.*
	...**

:bi-pond: (p1)
	.**....
	*..*...
	*..*...
	.**.**.
	...*..*
	...*..*
	....**.

:bi-ship:  = {ship-tie}

:bistable switch:  A {Spartan} {memory cell} found by Paul Callahan in
   1994.  It can be in one of two states, containing either a {boat} or
   a {block}. Input gliders on the appropriate paths can change the boat
   to a block, or vice-versa, while also emitting an output glider.
   Unlike many memory cells, attempts to change the state to the one it
   is already in are ignored with the glider passing through with no
   reaction.  This makes it easy to reset the memory cell to a known
   state.  Which of the two states is considered the SET and which
   considered the RESET is just a matter of convention.
     The pattern below shows the "boat" state of the memory cell in its
   original 1994 form.  Two gliders are also shown to indicate the input
   paths used to change the states.  A smaller version is shown under
   {century eater}, with the circuit in its "block" state.
     As shown, the rightmost glider changes the state from a boat to a
   block and emits a glider to the upper right, while the leftmost
   glider passes through unchanged.  Alternatively, when the state
   contains a block, then the leftmost glider changes the state from a
   block to a boat, and emits a glider to the lower right, while the
   rightmost glider passes through unchanged.
	................................*........................
	................................***......................
	...................................*.....................
	..................................**.....................
	.*.......................................................
	..*........................**.................**.........
	***.........................*.................*..........
	............................*.*.............*.*..........
	.............................**.............**...........
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.....................................*...................
	....................................*.*..................
	....................................*.*..................
	.....................................*...................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	...........................................*...........**
	............................................*..........**
	..........................................***............
	.........................................................
	.........................................................
	...........................................*.............
	..........................................*.*............
	...........................................**............
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	...............................**........................
	..............................*.*........................
	..............................*..........................
	.............................**..........................

:bit:  A live {cell}, if used in reference to {still life} {population}.
   For example, a {beehive} is a 6-bit still life.  Other uses generally
   involve information storage:  a {memory cell} such as a {honey bit}
   that can hold one binary bit of information for later retrieval.

:biting off more than they can chew: (p3)  Found by Peter Raynham, July
   1972.
	*...........
	***.........
	...*........
	..**........
	...**.......
	....**......
	...*..*.....
	...*..**....
	....**.***..
	........*.*.
	..........*.
	..........**

:Black&White:  = {Immigration}

:blasting cap:  The {pi-heptomino} (after the shape at generation 1). A
   term used at MIT and still occasionally encountered.

:blinker: (p2)  The smallest and most common {oscillator}.  Found by
   Conway, March 1970.
	***

:blinker fuse:  A {clean} {fuse} made from a row of blinkers separated
   by one cell gaps.  The blinker row {wick} is usually created by a
   {blinker puffer}.  The fuse can {burn} in at least three different
   ways at a speed of {2c/3} depending on the method used to ignite the
   end of the row of blinkers. This variant has found the most use.  The
   burning advances 12 cells every 18 generations.
	....................................................*.
	.............................................**.*..*.*
	............................................*.*.****.*
	***.***.***.***.***.***.***.***.***.***.***.*.........
	............................................*.*.****.*
	.............................................**.*..*.*
	....................................................*.
   Fuses can also be made with blinker rows which contain occasional two
   cell gaps, since the burning reaction is able to bridge those gaps.

:blinker puffer:  Any {puffer} whose output is {blinker}s.  However, the
   term is particularly used for p8 c/2 puffers.  The first such blinker
   puffer was found by Robert Wainwright in 1984, and was unexpectedly
   simple:
	...*.....
	.*...*...
	*........
	*....*...
	*****....
	.........
	.........
	.........
	.**......
	**.***...
	.****....
	..**.....
	.........
	.....**..
	...*....*
	..*......
	..*.....*
	..******.
   Since then many more blinker puffers have been found.  The following
   one was found by David Bell in 1992 when he was trying to extend an
   {x66}:
	.............***.
	............*****
	...........**.***
	............**...
	.................
	.................
	.........*.*.....
	..*.....*..*.....
	.*****...*.*.....
	**...**.**.......
	.*.......*.......
	..**..*..*.......
	..........*......
	..**..*..*.......
	.*.......*.......
	**...**.**.......
	.*****...*.*.....
	..*.....*..*.....
	.........*.*.....
	.................
	.................
	............**...
	...........**.***
	............*****
	.............***.
   The importance of this larger blinker puffer (and others like it), is
   that the engine which produces the blinker output is only p4.  The
   blinker row produced by the puffer can easily be ignited, and the
   resulting {blinker fuse} burns cleanly with a speed of 2c/3.  When
   the burning catches up to the engine, it causes a {phase change} in
   the puffer.  This fact allows p8 blinker puffers to be used to
   construct rakes of all periods which are large multiples of four.

:blinker pull:  The following glider/blinker collision, which moves a
   blinker (-1,3) toward the glider source:
	***.
	....
	....
	....
	.***
	.*..
	..*.

:blinkers bit pole: (p2)  Found by Robert Wainwright, June 1977.
	.....**
	***.*.*
	.......
	.*.*..*
	*....*.
	**...*.

:blinker ship:  A {growing spaceship} in which the wick consists of a
   line of {blinker}s.  An example by Paul Schick based on his
   {Schick engine} is shown below.  Here the front part is p12 and moves
   at c/2, while the back part is p26 and moves at 6c/13.  Every 156
   generations 13 blinkers are created and 12 are destroyed, so the wick
   becomes one blinker longer.
	..........****.............
	..........*...*............
	..........*................
	.**........*..*............
	**.**......................
	.****...*..................
	..**...*.**........*....***
	......*...*........*....*.*
	..**...*.**........*....***
	.****...*..................
	**.**......................
	.**........*..*............
	..........*................
	..........*...*............
	..........****.............

:block: (p1)  The most common {still life}, and also the most common
   object produced by {2-glider collision}s (six different ways).
	**
	**
   This can be used as a {catalyst} in many reactions.  For examples, it
   can destroy the {beehive} produced by the {queen bee shuttle} and can
   destroy an evolving {honey farm}:
	..*.*....
	..**.....
	...*.....
	.........
	.......**
	***....**
	..*......
	.*.......

:blockade: (p1)  A common formation of four blocks.  The final form of
   {lumps of muck}.
	**.....................
	**.....................
	.......................
	.......................
	.**.................**.
	.**.................**.
	.......................
	.......................
	.....................**
	.....................**

:block and dock: (p1)
	...**.
	...**.
	......
	.****.
	*....*
	**..**

:block and glider: (stabilizes at time 106)
	**..
	*.*.
	..**

:blocker: (p8)  Found by Robert Wainwright.  See also {filter}.
	......*.*.
	.....*....
	**..*....*
	**.*..*.**
	....**....

:block factory:  Any {factory} {circuit} that produces a {block} in
   response to an input signal.  For a useful high-{clearance} example
   see {keeper}.

:Blockic:  Adjective for {constellation}s consisting entirely of
   {block}s.  It's possible to arrange blocks in a way that can be
   {trigger}ed by a single glider to produce any {glider constructible}
   pattern.  A simple example of a Blockic pattern is shown under
   {fuse}.  See also {seed}.

:block keeper:  See {keeper}.

:block-laying switch engine:  See {stabilized switch engine}.

:block on big table:  = {block and dock}

:block on table: (p1)
	..**
	..**
	....
	****
	*..*

:block pull:  The following glider/block collision, which moves a block
   (2,1) toward the glider source.  Performing this reaction twice using
   a {salvo} of two gliders can move a block diagonally back by three
   cells, which can be of use for a {sliding block memory}.
	**.
	**.
	...
	...
	...
	...
	***
	*..
	.*.

:block pusher:  A pattern emitting streams of {glider}s which can
   repeatedly push a block further away.  This can be used as part of a
   {sliding block memory}.
     The following pattern, in which three gliders push a block one cell
   diagonally, is an example of how a block pusher works.
	...................*.*
	...................**.
	....................*.
	......................
	......................
	......................
	...*..................
	..*...................
	..***.................
	......................
	......................
	......................
	......................
	**...*................
	**...*.*..............
	.....**...............
     A universal {construction elbow} recipe library is also likely to
   contain one or more block-pushing reactions, since blocks are
   commonly used as elbows.

:blom: (stabilizes at time 23314)  The following {methuselah}, found by
   Dean Hickerson in July 2002.
	*..........*
	.****......*
	..**.......*
	..........*.
	........*.*.

:blonk:  A {block} or a {blinker}.  This term is mainly used in the
   context of {sparse Life} and was coined by Rich Schroeppel in
   September 1992.

:blonker: (p6)  The following {oscillator}, found by Nicolay Beluchenko
   in April 2004.
	*..**....*..
	**..*.**.*..
	....*.*.....
	.....**.....
	.......*....
	.......*...*
	.........*.*
	..........*.

:BLSE:  = {block-laying switch engine}

:BNE14T30:  A {B-heptomino} to {glider} {converter} found by Tanner
   Jacobi on 26 May 2016.  This converter has the unusual property of
   being an {edge shooter} where no part of the reaction's {envelope}
   extends beyond the glider's output {lane}.  It can be easily
   connected to {Herschel circuit}ry via {HFx58B} or other known
   {elementary} conduits.
	...........**....
	...........*.*...
	.............*...
	.......**...*.**.
	........*...*...*
	........*.**.**.*
	.........*.*.*.*.
	.................
	.................
	.................
	.................
	.................
	*................
	.*...............
	.**..............
	**...............
	*................
	.................
	.................
	.................
	**...............
	**...............

:boat: (p1)  The only 5-cell {still life}.
	**.
	*.*
	.*.
   A boat can be used as a 90-degree {one-time} {turner}.

:boat-bit:  A binary digit represented by the presence of a {boat} next
   to a {snake} (or other suitable object, such as an
   {aircraft carrier}).  The bit can be toggled by a {glider} travelling
   along a certain path.  A correctly timed glider on a crossing path
   can detect whether the transition was from 1 to 0 (in which case the
   crossing glider is deleted) or from 0 to 1 (in which case it passes
   unharmed).  Three gliders therefore suffice for a
   {non-destructive read}.  The mechanisms involved are shown in the
   diagram below.  Here the bit is shown in state 0.  It is about to be
   set to 1 and then switched back to 0 again.  The first crossing
   glider will survive, but the second will be destroyed.
	......*..................
	.......*.................
	.....***.................
	.........................
	.........................
	.........................
	.........................
	.........................
	.........................
	.........................
	................*........
	..............*.*........
	..........**...**........
	...........**............
	..........*..........*.**
	.....................**.*
	.........................
	.........................
	.........................
	.........................
	.........................
	.*.......................
	.**......................
	*.*......................
     In January 1997 David Bell found a method of reading the bit while
   setting it to 0.  A {MWSS} is fired at the boat-bit.  If it is
   already 0 (absent) then the MWSS passes unharmed, but if it is 1
   (present) then the boat and the MWSS are destroyed and, with the help
   of an {eater1}, converted into a glider which travels back along
   exactly the same path that is used by the gliders that toggle the
   boat-bit.
	................................................*........
	................................................***......
	...................................................*.....
	..................................................**.....
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	..*......................................................
	*...*..............................................*.....
	.....*..............................*****...........*....
	*....*.............................*....*.........***....
	.*****..................................*................
	...................................*...*.................
	.....................................*...................
	.........................................................
	.........................................................
	.......................................................**
	........................................................*
	.......................................................*.
	.......................................................**
   There are many other equivalent methods based on alternate incoming
   test {signal}s.

:boat maker: (c p4 fuse)
	................**
	...............*.*
	..............*...
	.............*....
	............*.....
	...........*......
	..........*.......
	.........*........
	........*.........
	.......*..........
	......*...........
	.....*............
	*****.............
	....*.............
	....*.............
	....*.............
	....*.............

:boat on boat:  = {boat-tie}

:boat-ship-tie:  = {ship tie boat}

:boatstretcher:  See {tubstretcher}.

:boat-tie: (p1)  A 10-cell {still life} consisting of two {boat}s placed
   tip-to-tip.  The name is a pun on "bow tie".
	.*....
	*.*...
	.**...
	...**.
	...*.*
	....*.

:bobsled:  = {switch engine channel}.

:boojum reflector: (p1)  Dave Greene's name for the following 180-degree
   {glider} {reflector} which he found in April 2001, winning $100
   bounties offered by Alan Hensel and Dieter Leithner.  The name is
   taken from Lewis Carroll's _The Hunting of the Snark_, referring to
   the fact that a small 90-degree stable reflector was really what was
   wanted.  180-degree reflectors are relatively undesirable and have
   limited use in larger circuitry constructions.
     The boojum reflector was the smallest and fastest known stable
   reflector until the discovery of the {rectifier} in 2009, followed by
   the {Snark} in 2013.
	....*.*......**.............................
	.....**......**.............................
	.....*......................................
	............................................
	............................................
	............................................
	............................................
	............................................
	............................................
	........................................*...
	.......................................*.*..
	.......................................*.*..
	....................**................**.**.
	....................**......................
	......................................**.**.
	..**..................................**.*..
	.*.*.......................................*
	.*........................................**
	**..........................................
	............................................
	..................................**........
	..................................**....**..
	...........**...........................*.*.
	..........*.*.............................*.
	..........*...............................**
	.........**.......................**........
	..................................**........
	............................................
	............................................
	.............................*..............
	............................*.*.............
	.............................*..............

:bookend:  The following {induction coil}.  It is generation 1 of
   {century}.
	..**
	*..*
	***.

:bookends: (p1)
	**...**
	*.*.*.*
	..*.*..
	.**.**.

:boss: (p4)  Found by Dave Buckingham, 1972.
	.....*.....
	....*.*....
	....*.*....
	...**.**...
	..*.....*..
	.*.*.*.*.*.
	.*.*...*.*.
	**.*...*.**
	*..*.*.*..*
	..*.....*..
	...**.**...
	....*.*....
	....*.*....
	.....*.....

:bottle: (p8)  Found by Achim Flammenkamp in August 1994.  The name is a
   back-formation from {ship in a bottle}.
	....**......**....
	...*..*....*..*...
	...*.*......*.*...
	.**..***..***..**.
	*......*..*......*
	*.**..........**.*
	.*.*..........*.*.
	...**........**...
	..................
	..................
	...**........**...
	.*.*..........*.*.
	*.**..........**.*
	*......*..*......*
	.**..***..***..**.
	...*.*......*.*...
	...*..*....*..*...
	....**......**....

:bouncer:  A label used for the small periodic {colour-changing}
   {glider} {reflector}s discovered mainly by Noam Elkies in the late
   1990s.  See  {p5 bouncer}, {p6 bouncer}, {p7 bouncer}, {p8 bouncer},
   or {p15 bouncer}.

:bounding box:  The smallest rectangular array of cells that contains
   the whole of a given pattern.  For {oscillator}s and {gun}s this
   usually is meant to include all {phase}s of the pattern, but in the
   case of guns, the outgoing stream(s) are excluded.  The bounding box
   is one of the standard ways to measure the size of an object; the
   other standard metric is the {population}.

:bow tie:  = {boat-tie}

:brain: (c/3 orthogonally, p3)  Found by David Bell, May 1992.
	.***.........***.
	*.*.**.....**.*.*
	*.*.*.......*.*.*
	.*.**.**.**.**.*.
	.....*.*.*.*.....
	...*.*.*.*.*.*...
	..**.*.*.*.*.**..
	..***..*.*..***..
	..**..*...*..**..
	.*....**.**....*.
	.*.............*.

:branching spaceship:  An {extensible} spaceship containing {component}s
   which can be attached in multiple ways so that the result can contain
   arbitrarily many {arm}s arranged like a binary tree.  Here is an
   example of a period 2 c/2 branching spaceship, which also includes a
   {wicktrailer}:
	.....................*.................*......................
	....................***...............***.....................
	..................**.***.............***.**...................
	...................*..*.**....*....**.*..*....................
	................**.*....*.*.**.**.*.*....*.**.................
	................**.*.*..*.*.......*.*..*.*.**.................
	................*........***.*.*.***........*....***..........
	...............**.......**.........**.......**..*...*.........
	...............*...............................*....**........
	........***....****.........................****..**.*........
	.......*...*..**..**..........................*.*....**.......
	......**....*......*....***.........................*.........
	......*.**..****...**..*...*..........................***.....
	.....**....*.*........*....**...........................**....
	.......*...........****..**.*............................*....
	...***...............*.*....**...........................**...
	..**.......................*..................................
	..*..........................***..............................
	.**............................**.............................
	.*..............................*....***......................
	.****...........................**..*...*.....................
	**..**.............................*....**....................
	.....*....***...................****..**.*....................
	.....**..*...*....................*.*....**...................
	........*....**.........................*.....................
	.....****..**.*...........................***.................
	.......*.*....**............................**................
	.............*...............................*................
	...............***...........................**...............
	.................**...........................*...............
	..................*........................****....***........
	..................**......................**..**..*...*.......
	...................*...............***....*......*....**......
	................****..............*...*..**...****..**.*......
	...............**..**............**....*........*.*....**.....
	...............*.................*.**..****...........*.......
	..............**................**....*.*...............***...
	..............*...................*.......................**..
	..............****............***..........................*..
	.............**..**..........**............................**.
	..................*..........*..............................*.
	..................**........**...........................****.
	...................*........*...........................**..**
	................****........****........................*.....
	...............**..**......**..**......................**.....
	...............*................*......................*......
	..............**................**.....................****...
	..............*.......................................**..**..
	..............****.........................................*..
	.............**..**........................................**.
	..................*...........................................
	..................**..........................................
   Branching spaceships have also been constructed for other speeds,
   such as c/3.

:breeder:  Any pattern whose {population} grows at a quadratic rate,
   although it is usual to exclude {spacefiller}s.  It is easy to see
   that this is the fastest possible growth rate.
     The term is also sometimes used to mean specifically the breeder
   created by Bill Gosper's group at MIT, which was the first known
   pattern exhibiting {superlinear growth}.
     There are four common types of breeder, known as MMM, MMS, MSM and
   SMM (where M=moving and S=stationary).  Typically an MMM breeder is a
   {rake} {puffer}, an MMS breeder is a puffer producing puffers which
   produce stationary objects ({still life}s and/or {oscillator}s), an
   MSM breeder is a {gun} puffer and an SMM breeder is a rake gun. There
   are, however, less obvious variants of these types.  Other less
   common breeder categories (SSS, hybrid MSS/MSM, etc.) can be created
   with some difficulty, based on {universal constructor} technology;
   see {Pianola breeder}.
     The original breeder was of type MSM (a p64 puffer puffing p30
   glider guns).  The known breeder with the smallest initial population
   is {switch-engine ping-pong}.

:bridge:  A term used in naming certain {still life}s (and the {stator}
   part of certain {oscillator}s).  It indicates that the object
   consists of two smaller objects joined edge to edge, as in
   {snake bridge snake}.

:broken lines:  A pattern constructed by Dean Hickerson in May 2005
   which produces complex broken lines of gliders and blocks.

:broth:  = {soup}

:BRx46B:  A {Spartan} {elementary conduit} discovered by Michael Simkin
   on 25 April 2016, one of the relatively few known conduits that can
   move a {B-heptomino} input to a B-heptomino output without an
   intervening {Herschel} stage.
	...........**
	..**.......**
	..**.........
	.............
	.............
	*..........*.
	.*........*.*
	.**.......*.*
	**.........*.
	*............

:BTC:  = {billiard table configuration}

:B track:  A {track} for {B-heptomino}es.  A B-heptomino becomes a
   {Herschel} plus a {block} in twenty generations, so this term was
   nearly synonymous with {Herschel track} until the discovery of
   {elementary conduit}s that convert a B directly to another B, or to
   some other non-Herschel signal output.  See for example {BRx46B}.

:BTS:  A 19-cell {still life} made up of a {bookend}, a {table}, and a
   {snake}.  Starting in 2015, with the help of Mike Playle's {Bellman}
   search program, Tanner Jacobi discovered a surprising number of ways
   to use this object as a {catalyst} for {signal} {circuit}ry.  One
   example can be seen in the {CC semi-cenark} entry.
	..**...
	*..*...
	***....
	.......
	**.*.**
	.*.**.*
	.*.....
	**.....

:buckaroo: (p30)   A {queen bee shuttle} stabilized at one end by an
   eater in such a way that it can turn a glider, as shown below.  The
   glider turning reaction uses a {banana spark} and is
   {colour-preserving}.  The mechanism was found by Dave Buckingham in
   the 1970s.  The name is due to Bill Gosper.
	..*.....................
	*.*.....................
	.**.....................
	...........*............
	.........*.*............
	........*.*.............
	.......*..*...........**
	........*.*...........**
	...**....*.*............
	..*.*......*............
	..*.....................
	.**.....................

:bullet heptomino:  Generation 1 of the {T-tetromino}.
	.*.
	***
	***

:bumper:  One of several periodic {colour-preserving} {glider}
   {reflector}s discovered by Tanner Jacobi on 6 April 2016.  See
   {p3 bumper}, {p4 bumper}, {p5 bumper}, {p6 bumper}, {p7 bumper},
   {p8 bumper}, {p9 bumper}, {p11 bumper}, and {p15 bumper}.

:bun:  The following {induction coil}.  By itself this is a common
   {predecessor} of the {honey farm}.  See also {cis-mirrored R-bee}.
	.**.
	*..*
	.***

:bunnies: (stabilizes at time 17332)  This is a {parent} of {rabbits}
   and was found independently by Robert Wainwright and Andrew
   Trevorrow.
	*.....*.
	..*...*.
	..*..*.*
	.*.*....

:burloaf:  = {loaf}

:burloaferimeter: (p7)  Found by Dave Buckingham in 1972.  See also
   {airforce}.
	....**....
	.....*....
	....*.....
	...*.***..
	...*.*..*.
	**.*...*.*
	**.*....*.
	....****..
	..........
	....**....
	....**....

:burn:  A reaction which travels indefinitely as a {wave} through the
   components of a {wick} or an {agar}.  A burning wick is known as a
   {fuse}.
     If the object being burned has a spatial periodicity, then the
   active area of the burning usually remains bounded and so eventually
   develops a periodicity too.  It is unknown whether this will always
   occur.
     The speed of burning can range from arbitrarily slow up to the
   {speed of light}.  The results of burning can be clean (leaving no
   debris), or leaving debris usually much different from the original
   object.  In rare cases, a {reburnable fuse} produces an exact copy of
   the original object, allowing the creation of objects such as the
   {telegraph}.
     In many useful cases burning can be initiated by impacting an
   object with {glider}s or other {spaceship}s.  An object might be able
   to burn in more than one way, depending on how the burn is initiated.

:bushing:  That part of the {stator} of an {oscillator} which is
   adjacent to the {rotor}.  Compare {casing}.

:butterfly:  The following pattern, or the formation of two beehives
   that it evolves into after 33 generations.  (Compare {teardrop},
   where the beehives are five cells closer together.)
	*...
	**..
	*.*.
	.***

:Bx125:  An {elementary conduit}, one of the original sixteen
   {Herschel conduit}s, discovered by Paul Callahan in November 1998.
   After 125 ticks, it produces an inverted {Herschel} rotated 180
   degrees at (-9, -17) relative to the input.  Its {recovery time} is
   166 ticks.  A {ghost Herschel} in the pattern below marks the output
   location:
	...........................*..........
	..*.......................*.*.........
	..*.......................*.*.........
	***.........**...........**.***.......
	*...........**.................*......
	.........................**.***.......
	.........................**.*.........
	......................................
	......................................
	......................................
	......................................
	......................................
	......................................
	......................................
	......................................
	....................................**
	....................................**
	......................................
	.........*............................
	.........*.*..........................
	.........***..........................
	...........*..........................
	......................................
	.......................**.............
	.......................*..............
	........................***...........
	..........................*...........

:Bx222:  A {composite conduit}, one of the original sixteen
   {Herschel conduit}s, discovered by Paul Callahan in October 1998.  It
   is made up of three {elementary conduit}s, HF95P + PB68B + {BFx59H}.
   After 222 ticks, it produces a mirror-reflected {Herschel} rotated
   180 degrees, at (6, -16) relative to the input.  Its {recovery time}
   is 271 ticks.  A {ghost Herschel} in the pattern below marks the
   output location:
	.............*............................
	....**.....***.......**...................
	.....*....*..........*....................
	.....*.*...*..........*...................
	......*.*...*........**...................
	.......*...**.................*......*....
	............................***.....*.*...
	...........................*........*.*...
	...........................**......**.***.
	.........................................*
	..*...............**...............**.***.
	..*...............**...............**.*...
	***.......................................
	*.........................................
	..........................................
	..........................................
	........................................**
	........................................*.
	......................................*.*.
	......................................**..
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	......*...................................
	......*.*.................................
	......***.................................
	........*....................**...........
	.............................*............
	..................**..........*...........
	..................**..**.....**...........
	......................*.*.................
	........................*.................
	........................**................

:by flops: (p2)  Found by Robert Wainwright.
	...*..
	.*.*..
	.....*
	*****.
	.....*
	.*.*..
	...*..

:c:  = {speed of light}

:c/10 spaceship:  A {spaceship} travelling at one tenth of the
   {speed of light}.  The first such spaceship to be discovered was the
   orthogonally travelling {copperhead}, found by 'zdr' on 5 March 2016.
   Simon Ekstrom found the related {fireship} two weeks later.  A
   {Caterloopillar} can theoretically be configured to move at c/10, but
   there are technical difficulties with speeds of the form 4n+2, and as
   of June 2018 this has not been done in practice.

:c/12 spaceship:  A {spaceship} travelling at one twelfth of the
   {speed of light}.  The only diagonal spaceships that are currently
   known to move at this speed are the {Cordership}s.  An orthogonal
   {Caterloopillar} has been configured to move at c/12.

:c/2 spaceship:  A {spaceship} travelling at half the {speed of light}.
   Such spaceships necessarily move orthogonally.  The first to be
   discovered was the {LWSS}.  For other examples see {Coe ship},
   {ecologist}, {flotilla}, {hammerhead}, {hivenudger}, {HWSS}, {MWSS},
   {puffer train}, {puff suppressor}, {pushalong}, {Schick engine},
   {sidecar}, {still life tagalong} and {x66}.

:c/3 spaceship:  A {spaceship} travelling at one third of the
   {speed of light}.  All known c/3 spaceships travel orthogonally.  The
   first was {25P3H1V0.1}, found in August 1989 by Dean Hickerson.  For
   further examples see {brain}, {dart}, {edge-repair spaceship}, {fly},
   {turtle} and {wasp}.

:c/4 spaceship:  A {spaceship} travelling at one quarter of the
   {speed of light}.  The first such spaceship to be discovered was, of
   course, the {glider}, and this remained the only known example until
   December 1989, when Dean Hickerson found the first orthogonal
   example, {119P4H1V0}, and also a new diagonal example (the
   {big glider}). For other examples see {B29}, {Canada goose}, {crane},
   {Enterprise}, {edge-repair spaceship} (third pattern),
   {non-monotonic}, {Orion}, {quarter}, {sparky}, {swan} and {tagalong}.
   It is known that c/4 is the fastest possible speed for a (45-degree)
   diagonal spaceship.

:c/5 spaceship:  A {spaceship} travelling at one fifth of the
   {speed of light}.  The first such spaceship to be discovered was the
   {snail}, found by Tim Coe in January 1996.  The first diagonally
   moving example, {295P5H1V1}, was found by Jason Summers in November
   2000.  For other c/5 ships see {58P5H1V1}, {67P5H1V1}, {86P5H1V1} and
   {spider}.  A {Caterloopillar} has also been configured to move at
   c/5.

:c/6 spaceship:  A {spaceship} travelling at one sixth of the
   {speed of light}.  The first such spaceship to be discovered was the
   {dragon}, found by Paul Tooke in April 2000.  The first diagonally
   moving example was the {seal}, found by Nicolay Beluchenko in
   September 2005.  Another orthogonal c/6 spaceship, found by Paul
   Tooke in March 2006, is shown below.  For the smallest known c/6
   spaceship see {56P6H1V0}.
	..*..............*..................................*.....
	*..*..***.......*.****...............**...........**.*....
	*..*............***.*.*.........*.....*.......*...*.......
	.*.*..*.....................***..*.*.***.....*.*.*....*...
	..**......*....*................******..*..*...*...*..*...
	.*.*...**.....*...**......**.**..*..**..*.*.**..*.........
	..*.....*.**..*...**......**....*.*.*..*..*.*.*......**..*
	..*....***..*.........***.......***.*.**.....*.......***.*
	............*********...*........**.***...****.........*.*
	..........................................................
	............*********...*........**.***...****.........*.*
	..*....***..*.........***.......***.*.**.....*.......***.*
	..*.....*.**..*...**......**....*.*.*..*..*.*.*......**..*
	.*.*...**.....*...**......**.**..*..**..*.*.**..*.........
	..**......*....*................******..*..*...*...*..*...
	.*.*..*.....................***..*.*.***.....*.*.*....*...
	*..*............***.*.*.........*.....*.......*...*.......
	*..*..***.......*.****...............**...........**.*....
	..*..............*..................................*.....
   A {Caterloopillar} can theoretically be configured to move at c/6,
   but there are technical difficulties with speeds of the form 4n+2,
   and as of July 2018 this has not been done in practice.

:c/7 spaceship:  A {spaceship} travelling at one seventh of the
   {speed of light}.  The first such spaceship to be discovered was the
   diagonally travelling {lobster}, found by Matthias Merzenich in
   August 2011.  The first known orthogonal c/7 spaceship was the
   {loafer}, discovered by Josh Ball in February 2013.  A
   {Caterloopillar} has been configured to move at c/7.

:CA:  = {cellular automaton}

:caber tosser:  Any pattern whose {population} is asymptotic to c.log(t)
   for some constant c, and which contains a {glider} (or other
   {spaceship}) bouncing between a slower receding spaceship and a fixed
   {reflector} which emits a spaceship (in addition to the reflected
   one) whenever the bouncing spaceship hits it.
     As the receding spaceship gets further away the bouncing spaceship
   takes longer to complete each cycle, and so the extra spaceships
   emitted by the reflector are produced at increasingly large
   intervals.  More precisely, if v is the speed of the bouncing
   spaceship and u the speed of the receding spaceship, then each
   interval is (v+u)/(v-u) times as long as the previous one.  The
   population at time t is therefore n.log(t)/log((v+u)/(v-u)) + O(1),
   where n is the population of one of the extra spaceships (assumed
   constant).
     The first caber tosser was built by Dean Hickerson in May 1991.

:Callahan G-to-H:  A stable {glider reflector} and glider-to-Herschel
   {converter} discovered by Paul Callahan in November 1998.  Its
   recovery time is 575 ticks.  The initial stage converts two gliders
   into a Herschel.  A {ghost Herschel} in the pattern below marks the
   output location:
	....*.........*...................
	....***.....***...................
	.*.....*...*......................
	..*...**...**.....................
	***...............................
	.........*........................
	........*.*.......................
	........*.*.......................
	.........*........................
	...............................*..
	...............................*..
	....................**.........***
	..............**....**...........*
	........**...**...................
	.......*..*....*..................
	..**....**........................
	.*.*..............................
	.*................................
	**................................
	..........**......................
	..........*.......................
	...........***....................
	.............*....................
     The glider from the southeast can be supplied by an {Fx77} + {L112}
   + Fx77 Herschel track, or by reflecting the output Herschel's {FNG}
   as in the {p8 G-to-H}.  See also {Silver reflector}, {Silver G-to-H}.

:Cambridge pulsar CP 48-56-72:  = {pulsar}  (The numbers refer to the
   populations of the three {phase}s.  The Life pulsar was indeed
   discovered at Cambridge, like the first real pulsar a few years
   earlier.)

:Canada goose: (c/4 diagonally, p4)  Found by Jason Summers, January
   1999.  It consists of a {glider} plus a {tagalong}.
	***..........
	*.........**.
	.*......***.*
	...**..**....
	....*........
	........*....
	....**...*...
	...*.*.**....
	...*.*..*.**.
	..*....**....
	..**.........
	..**.........
   At the time of its discovery the Canada goose was the smallest known
   diagonal {spaceship} other than the glider, but this record has since
   been beaten, first by the second spaceship shown under {Orion}, and
   more recently by {quarter}.

:candelabra: (p3)  By Charles Trawick.  See also the note under {cap}.
	....**....**....
	.*..*......*..*.
	*.*.*......*.*.*
	.*..*.****.*..*.
	....*.*..*.*....
	.....*....*.....

:candlefrobra: (p3)  Found by Robert Wainwright in November 1984.
	.....*....
	.*.**.*.**
	*.*...*.**
	.*....*...
	.....**...
   The following diagram shows that a pair of these can act in some ways
   like {killer toads}.  See also {snacker}.
	....*...........*....
	**.*.**.*...*.**.*.**
	**.*...*.*.*.*...*.**
	...*....*...*....*...
	...**...........**...
	.....................
	.....................
	.........***.........
	.........*..*........
	.........*...........
	.........*...*.......
	.........*...*.......
	.........*...........
	..........*.*........

:canoe: (p1)
	...**
	....*
	...*.
	*.*..
	**...

:cap:  The following {induction coil}.  It can also easily be stabilized
   to form a p3 oscillator.  See {candelabra} for a slight variation on
   this.
	.**.
	*..*
	****

:carnival shuttle: (p12)  Found by Robert Wainwright in September 1984
   (using {MW emulator}s at the end, instead of the {monogram}s shown
   here).
	.................................*...*
	**...**..........................*****
	.*.*.*...*..*......**...*..*.......*..
	.**.**..**...**....**..**...**....*.*.
	.*.*.*...*..*......**...*..*.......*..
	**...**..........................*****
	.................................*...*

:carrier:  = {aircraft carrier}

:casing:  That part of the {stator} of an {oscillator} which is not
   adjacent to the {rotor}.  Compare {bushing}.

:catacryst:  A 58-cell {quadratic growth} pattern found by Nick Gotts in
   April 2000.  This was formerly the smallest such pattern known, but
   has since been superseded by the related {metacatacryst}.  See
   {switch-engine ping-pong} for the lowest-population
   {superlinear growth} pattern as of July 2018, along with a list of
   the record-holders.
     The catacryst consists of three {ark}s plus a glider-producing
   {switch engine}.  It produces a block-laying switch engine every
   47616 generations.  Each block-laying switch engine has only a finite
   life, but the length of this life increases linearly with each new
   switch engine, so that the pattern overall grows quadratically, as an
   unusual type of MMS {breeder}.

:Catagolue:  An online database of objects in Conway's Game of Life and
   similar cellular automata, set up by Adam P. Goucher in 2015 at
   {http://catagolue.appspot.com}. It gathers data from a distributed
   search of random initial configurations and records the eventual
   decay products.  Within a year of operation it had completed a
   {census} of the {ash} objects from over two trillion asymmetric 16x16
   {soup}s.  As of June 2018, well over two hundred trillion ash objects
   have been counted, from over a trillion asymmetric soups.
     It is often possible to use Catagolue search results find
   equivalent {glider synthesis} recipes for selected parts of
   long-running active reactions.  These random {soup} searches have
   made it possible to find efficient construction methods for thousands
   of increasingly rare {still life}s and {oscillator}s, and the
   occasional {puffer} or {spaceship}.  In many of these cases a
   {glider synthesis} was previously very difficult or unknown.

:catalyst:  An object that participates in a reaction but emerges from
   it unharmed.  All {eater}s are catalysts.  Some small {still life}s
   can act as catalysts in some situations, such as the {block}, {ship},
   and {tub}.  The still lifes and oscillators that form a {conduit} are
   examples of catalysts.
     A relatively rare form of catalysis occurs in a
   {transparent debris effect}, where the catalyst in question is
   completely destroyed and then rebuilt.  The term is also sometimes
   used for a modification of an active reaction in a {rake} by passing
   {spaceship}s.

:catch and throw:  A {technology} used (e.g., in the {Caterpillar}) to
   adjust the timing of a glider by turning it into a stationary object
   using one interaction, and then later restoring it using a second
   interaction.  The interactions are caused by passing objects which
   are not otherwise affected.  The direction of the glider is not
   usually changed.
     Here is an example where a glider is turned into a {boat} by the
   first {LWSS}, and is then restored by the remaining {spaceship}s:
	..................................**.............**.......****.
	................................*....*..........**.****...*...*
	...............................*.................******...*....
	...............................*.....*............****.....*..*
	.*.............................******..........................
	..*............................................................
	***............................................................
	...............................................................
	...............................................................
	...............................................................
	...............................................................
	...............................................................
	...****........................................................
	...*...*.......................................................
	...*...........................**..............................
	....*..*......................**.***...........................
	...............................*****...........................
	................................***............................

:caterer: (p3)  Found by Dean Hickerson, August 1989.  Compare with
   {jam}.  In terms of its minimum {population} of 12 this is the
   smallest p3 {oscillator}.  See also {double caterer} and
   {triple caterer}.
	..*.....
	*...****
	*...*...
	*.......
	...*....
	.**.....
   More generally, any oscillator which serves up a {bit} in the same
   manner may be referred to as a caterer.

:Caterloopillar:  A family of adjustable-speed {spaceship}s constructed
   by Michael Simkin in 2016, based on an "engineless caterpillar" idea
   originally proposed by David Bell.  The front and back halves of
   Caterloopillars each function as universal constructors, with each
   half constructing the building blocks of the other half, while also
   reading and moving a construction tape. The overall design is
   reminiscent of M.C. Escher's lithograph "Drawing Hands". The name
   "Caterloopillar" is a reference to Douglas Hofstader's Strange Loop
   concept.
     Simkin has written an automated script that can construct a
   Caterloopillar for any rational speed strictly less than c/4, with
   some exceptions.  Speeds closer to the c/4 limit in general require
   larger constructions, and for any given computer system it is easy to
   choose a speed that makes it impractical to construct a
   Caterloopillar.
     As of June 2018 one significant remaining exception is that
   Caterloopillars with periods c/(6+4N) can't be constructed.  This is
   only a limitation of the current construction script, not of the
   underlying Caterloopillar {toolkit}.  For technical reasons, the
   lowest speed that the current script can produce is around c/95.  The
   slowest Caterloopillars that have been explicitly constructed to date
   are c/87 and c/92.  These are among the smallest in terms of
   population, though their bounding boxes are larger than some of the
   higher-speed Caterloopillars.

:Caterpillar:  A {spaceship} that works by laying tracks at its front
   end.  The first example constructed was a p270 17c/45 spaceship built
   by Gabriel Nivasch in December 2004, based on work by himself, Jason
   Summers and David Bell.  This Caterpillar has a population of about
   12 million in each generation and was put together by a computer
   program that Nivasch wrote.  At the time it was by far the largest
   and most complex Life object ever constructed, and it is still one of
   the largest in terms of population.
     The 17c/45 Caterpillar is based on the following reaction between a
   {pi-heptomino} and a {blinker}:
	...............*
	*.............**
	*............**.
	*.............**
	...............*
   In this reaction, the pi moves forward 17 cells in the course of 45
   generations, while the blinker moves back 6 cells and is rephased.
   This reaction has been known for many years, but it was only in
   September 2002 that David Bell suggested that it could be used to
   build a 17c/45 spaceship, based on a reaction he had found in which
   pi-heptominoes crawling along two rows of blinkers interact to emit a
   glider every 45 generations.  Similar glider-emitting interactions
   were later found by Gabriel Nivasch and Jason Summers.  The basic
   idea of the spaceship design is that streams of gliders created in
   this way can be used to construct fleets of {standard spaceship}s
   which convey gliders to the front of the blinker tracks, where they
   can be used to build more blinkers.
     A different Caterpillar may be possible based on the following
   reaction, in which the pattern at top left reappears after 31
   generations displaced by (13,1), having produced a new NW-travelling
   glider.  In this case the tracks would be waves of backward-moving
   gliders.
	.**.....................
	...*....................
	...*.**.................
	***....*................
	.......*................
	.....***................
	........................
	........................
	........................
	........................
	........................
	........................
	.....................***
	.....................*..
	......................*.
   For other Caterpillar-type constructions see {Centipede},
   {waterbear}, {half-baked knightship}, and {Caterloopillar}.

:CatForce:  An optimized {search program} written by Michael Simkin in
   2015, using brute-force enumeration of small {Spartan} objects in a
   limited area, instead of a depth-first tree search.  One major
   purpose of CatForce is to find glider-constructible completions for
   signal conduits.  An early CatForce discovery was the {B60} conduit,
   which enabled a record-breaking new glider gun.

:Catherine wheel:  = {pinwheel}

:cauldron: (p8)  Found in 1971 independently by Don Woods and Robert
   Wainwright.  Compare with {Hertz oscillator}.
	.....*.....
	....*.*....
	.....*.....
	...........
	...*****...
	*.*.....*.*
	**.*...*.**
	...*...*...
	...*...*...
	....***....
	...........
	....**.*...
	....*.**...

:cavity:  = {eater plug}

:CC semi-cenark:  The {colour-changing} version of Tanner Jacobi's
   century-based semi-Snark mechanism, using a {C-to-G} consisting of a
   {BTS} {catalyst} and a {block}.  See {CP semi-cenark} for the
   {colour-preserving} version, or {semi-cenark} for repeat time details
   and an alternate initial catalyst.
	.*............**..........
	..*..........*.*..........
	***.....**..*.............
	........*..*.**...........
	.....*....**.*.*..........
	...*.*........*...........
	....**..............**....
	....................*.....
	.......**.........*.*.....
	.......**.........**......
	..........................
	..........................
	..........................
	....**....**..............
	...*.*...*.*..............
	...*......*...............
	..**......................
	..........................
	.....................**...
	...................*..*...
	...................***....
	..........................
	..............**...**.*.**
	..............**....*.**.*
	....................*.....
	...................**.....

:CC semi-Snark:  A small 90-degree {colour-changing} {glider reflector}
   requiring two input gliders on the same lane for each output glider.
   It was discovered by Sergei Petrov on 1 July 2013, using a
   custom-written search utility.  It functions as a very compact
   {period doubler} in some {signal} {circuit}ry, for example the
   {linear propagator}.  The semi-Snark can period-double a regular
   glider {stream} of period 51 or more, or an {intermittent stream}
   with two gliders every 67 ticks or more, since the block reset glider
   can be sent just 16 ticks before its partner.
	......*..........**
	.......**........*.
	......**.......*.*.
	...............**..
	..........*........
	**.........**......
	**........**.......
	...................
	...................
	.................**
	..........**.....**
	..........**.......
	...................
	.....*.............
	....*.*............
	....**......**.....
	............*......
	.............***...
	...............*...

:cell:  The fundamental unit of space in the Life universe.  The term is
   often used to mean a live cell - the sense is usually clear from the
   context.

:cellular automaton:  A certain class of mathematical objects of which
   {Life} is an example.  A cellular automaton consists of a number of
   things.  First there is a positive integer n which is the dimension
   of the cellular automaton.  Then there is a finite set of states S,
   with at least two members.  A state for the whole cellular automaton
   is obtained by assigning an element of S to each point of the
   n-dimensional lattice Z^n (where Z is the set of all integers). The
   points of Z^n are usually called cells.  The cellular automaton also
   has the concept of a neighbourhood.  The neighbourhood N of the
   origin is some finite (nonempty) subset of Z^n.  The neighbourhood of
   any other cell is obtained in the obvious way by translating that of
   the origin.  Finally there is a transition rule, which is a function
   from S^N to S (that is to say, for each possible state of the
   neighbourhood the transition rule specifies some cell state). The
   state of the cellular automaton evolves in discrete time, with the
   state of each cell at time t+1 being determined by the state of its
   neighbourhood at time t, in accordance with the transition rule.
     There are some variations on the above definition.  It is common to
   require that there be a quiescent state, that is, a state such that
   if the whole universe is in that state at generation 0 then it will
   remain so in generation 1.  (In Life the OFF state is quiescent, but
   the ON state is not.)  Other variations allow spaces other than Z^n,
   neighbourhoods that vary over space and/or time, probabilistic or
   other non-deterministic transition rules, etc.
     It is common for the neighbourhood of a cell to be the 3x...x3
   (hyper)cube centred on that cell.  (This includes those cases where
   the neighbourhood might more naturally be thought of as a proper
   subset of this cube.)   This is known as the Moore neighbourhood.

:census:  A count of the number of different individual Life objects
   within one larger object, most often the final {ash} of a random
   {soup} experiment.  This includes the number of {block}s, {blinker}s,
   {glider}s, and other common objects, as well as any rarer larger
   {still life}s, {oscillator}s or {spaceship}s.

:centinal: (p100)  Found by Bill Gosper.  This combines the mechanisms
   of the p46 and p54 shuttles (see {twin bees shuttle} and
   {p54 shuttle}).
	**................................................**
	.*................................................*.
	.*.*.....................**.....................*.*.
	..**........*............**............**.......**..
	...........**..........................*.*..........
	..........**.............................*..........
	...........**..**......................***..........
	....................................................
	....................................................
	....................................................
	...........**..**......................***..........
	..........**.............................*..........
	...........**..........................*.*..........
	..**........*............**............**.......**..
	.*.*.....................**.....................*.*.
	.*................................................*.
	**................................................**

:Centipede: (31c/240 orthogonally, p240)  The smallest known {31c/240}
   spaceship, constructed by Chris Cain in September 2014 as a
   refinement of the {shield bug}.

:century: (stabilizes at time 103)  This is a common pattern which
   evolves into three {block}s and a {blinker}.  In June 1996 Dave
   Buckingham built a neat {p246 gun} using a century as the engine.
   See also {bookend} and {diuresis}.
	..**
	***.
	.*..

:century eater:  A 20-cell {still life} that functions as an {eater} for
   the active reaction produced by any {century} relative.  The most
   well-known use is to replace a four-object {constellation} in Paul
   Callahan's {bistable switch}, as shown below.  In September 2014 Josh
   Ball showed that a variant of this still life has a relatively
   inexpensive {slow glider construction} {recipe}.
	............*.**..............
	............**.*..............
	..............................
	..........*****...............
	.........*..*..*..............
	.........**...*.*.............
	...............**.............
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	............................**
	............................**
	..............................
	*.............................
	.**...........................
	**............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	....**........................
	...*.*........................
	...*..........................
	..**........**................
	............**................
   At T=256 the active reaction produces an eight-cell pattern sharing
   the same grandchild as a century.  The century eater at the top of
   the pattern catalyzes this pattern produce a clean {spark}.

:century-to-glider converter:  Any {signal} {circuit} that accepts a
   {century} as input and produces a clean output {glider}.  For
   example, in November 2017 Adam P. Goucher noticed that this
   previously known C-to-G {converter} can replace the {century eater}
   in Paul Callahan's {bistable switch}, producing an extra glider
   output.
	......................**.......
	.......................*.......
	.......................*.*.....
	........................*.*....
	.........................*...**
	.............................**
	...............................
	...............................
	...............................
	...............................
	**.............................
	**.............................
	...............................
	...............................
	.....................*.........
	....................***........
	......................**.......

:channel:  A {lane} or {signal} path used in construction circuitry.
   Until the invention of {single-channel} {construction arm}s, signals
   in a channel would usually be {synchronized} with one or more
   coordinated signals on other paths, as in the {Gemini}, which used
   twelve channels to run three construction arms simultaneously, or the
   10hd {Demonoid} which needed only two channels.  See also {Geminoid}.

:chaotic growth:  An object whose {fate} is unknown, except that it
   appears to grow forever in an unpredictable manner.  In Life, no
   pattern has yet been found that is chaotic.  This is in contrast to
   many other Life-like rules, where even small objects can appear to
   grow chaotically.
     It is possible that chaotic growth may occur rarely or even
   regularly for large enough random Life objects, but if so the minimum
   size of such patterns must be larger than what can currently be
   experimentally simulated (but see {novelty generator}).
     In any case, it is not decidable whether a pattern that apparently
   grows randomly forever is in fact displaying chaotic growth.
   Continuing to evolve such a pattern might at any time result in it
   suddenly cleaning itself up and becoming predictable.

:chemist: (p5)
	.......*.......
	.......***.....
	..........*....
	.....***..*..**
	....*.*.*.*.*.*
	....*...*.*.*..
	.**.*.....*.**.
	..*.*.*...*....
	*.*.*.*.*.*....
	**..*..***.....
	....*..........
	.....***.......
	.......*.......

:C-heptomino:  Name given by Conway to the following {heptomino}, a less
   common variant of the {B-heptomino}.
	.***
	***.
	.*..

:Cheshire cat:  A block {predecessor} by C. R. Tompkins that
   unaccountably appeared both in Scientific American and in
   {Winning Ways}.  See also {grin}.
	.*..*.
	.****.
	*....*
	*.**.*
	*....*
	.****.

:chicken wire:  A type of {stable} {agar} of {density} 1/2.  The
   simplest version is formed from the tile:
	**..
	..**
   But the "wires" can have length greater than two and need not all be
   the same.  For example:
	**...****.....
	..***....*****

:chirality:  A term borrowed from chemistry to describe asymmetrical
   patterns with two distinct mirror-image orientations.  One common use
   is in relation to {Herschel transmitter}s, where the spacing between
   the two gliders in the {tandem glider} output can limit the
   {receiver} to a single chirality.

:cigar:  = {mango}

:circuit:  Any combination of {conduit}s or {converter}s that moves or
   processes an active {signal}.  This includes components with multiple
   states such as {period multiplier}s or {switch}es, which can be used
   to build {gun}s, logic gates, {universal constructor}s, and other
   computation or construction circuitry.

:cis-beacon on anvil: (p2)
	...**..
	....*..
	.*.....
	.**....
	.......
	.****..
	*....*.
	.***.*.
	...*.**

:cis-beacon on table: (p2)
	..**
	...*
	*...
	**..
	....
	****
	*..*

:cis-boat with tail: (p1)
	.*...
	*.*..
	**.*.
	...*.
	...**

:cis fuse with two tails: (p1)  See also {pulsar quadrant}.
	...*..
	.***..
	*...**
	.*..*.
	..*.*.
	...*..

:cis-mirrored R-bee: (p1)
	.**.**.
	*.*.*.*
	*.*.*.*
	.*...*.

:cis snake:  = {canoe}

:clean:  Opposite of {dirty}.  A reaction which produces a small number
   of different products which are desired or which are easily deleted
   is said to be clean.  For example, a {puffer} which produces just one
   object per period is clean.  Clean reactions are useful because they
   can be used as building blocks in larger constructions.
     When a {fuse} is said to be clean, or to {burn} cleanly, this
   usually means that no debris at all is left behind.

:clearance:  In signal circuitry, the distance from an {edge shooter}
   output {lane} to the last unobstructed lane adjacent to the
   edge-shooter circuitry.  For example, an {Fx119 inserter} has an
   unusually high 27{hd} clearance.
     Also, oscillator and eater variants may be said to have better
   clearance if they allow {glider}s or other {signal}s to pass closer
   to them than the standard variant allows.  The following
   high-clearance {eater1} variant by Karel Suhajda allows gliders to
   pass one lane closer on the southeast side, than is allowed by the
   standard fishhook shape.
	.*......**
	..*..**..*
	***...*.*.
	......*.**
	...**.*...
	...*..*...
	....**....
   This is considered to be a variant of the eater1 because the
   reaction's {rotor} is exactly the same, even though three cells in
   this variant are too overpopulated to allow a birth, instead of
   underpopulated as in a standard eater1 glider-eating reaction.

:clock: (p2)  Found by Simon Norton, May 1970.  This is the fifth or
   sixth most common {oscillator}, being about as frequent as the
   {pentadecathlon}, but much less frequent than the {blinker}, {toad},
   {beacon} or {pulsar}.  It is surprisingly rare considering its small
   size.
	..*.
	*.*.
	.*.*
	.*..
     The protruding cells at the edges can perturb some reactions by
   inhibiting the birth of a cell in a 3-cell corner.  For example, a
   clock can be used to suppress the surplus {blinker} produced by an
   {F171} conduit, significantly improving the {recovery time} of the
   circuit:
	.........*........*................................
	.........***......***..............................
	............*........*.............................
	...........**.......**.............................
	...................................................
	.................................................*.
	................................................*.*
	................................................*.*
	.................................................*.
	......................................*............
	............**........................*............
	.............*........................***..........
	.............*.*........................*..........
	..............**...................................
	...................................................
	...................................................
	........*..............................**..........
	........***........................*...**..........
	...........*......................*.*..............
	..........**.....................*.*...............
	.................................*.................
	................................**.................
	...................................................
	...................................................
	...................................................
	...................................................
	.........*.........................................
	.........*.*.......................................
	.........***.......................................
	...........*.......................................
	...................................................
	..................**...*...........................
	...................*....**.........................
	................***...**...........................
	..**............*.......*..........................
	...*...............................................
	***................................................
	*..................................................

:clock II: (p4)  Compare with {pinwheel}.
	......**....
	......**....
	............
	....****....
	**.*....*...
	**.*..*.*...
	...*..*.*.**
	...*.*..*.**
	....****....
	............
	....**......
	....**......

:clock inserter:  = {clock insertion}.

:clock insertion:  A uniquely effective method of adding a glider to the
   front edge of a {salvo}, by first constructing a {clock}, then
   converting it to a glider using a one-bit {spark}.  Here it rebuilds
   a sabotaged glider in a deep pocket between other gliders:
	..................................................*........
	..................................................*.*......
	..................................................**.......
	...............................................*......*....
	..............................................*......*.....
	..............................................***....***...
	...........................................................
	...........................................*......*........
	...........................................*.*....*.*.....*
	...........................................**.....**....**.
	........................................*.......*........**
	.......................................*...................
	.......................................***...........*.*...
	.....................................................**....
	......................................................*....
	*..................................................*.......
	.**..............................................**........
	**................................................**.......
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	.............................*.............................
	....................*......*.*.............................
	..................*.*.......**.............................
	...................**......................................
	.........................*.................................
	..........................*....***.........................
	........................***....*...........................
	................................*..........................
	.....................................**....................
	............................**.......*.*...................
	............................*.*......*.....................
	............................*..............................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	.............................................**............
	.............................................*.*...........
	.............................................*.............
     In 2015 Chris Cain used this reaction to demonstrate conclusively
   that any unidirectional glider {salvo}, no matter how large or
   tightly packed, can be constructed by collisions between gliders that
   are initially separated by any finite distance.  As a corollary,
   because all glider syntheses are made up of two to four
   unidirectional salvos, any glider-constructible object has a
   synthesis that starts with every glider at least N cells away from
   every other glider (for any chosen N).

:cloud of smoke:  = {smoke}

:cloverleaf:  This name was given by Robert Wainwright to his p2
   oscillator {washing machine}.  But Achim Flammenkamp also gave this
   name to {Achim's p4}.

:cluster:  Any pattern in which each live cell is connected to every
   other live cell by a path that does not pass through two consecutive
   dead cells.  This sense is due to Nick Gotts, but the term has also
   been used in other senses, often imprecise.

:CNWH:  Conweh, creator of the Life universe.

:Coe ship: (c/2 orthogonally, p16)  A {puffer engine} discovered by Tim
   Coe in October 1995.
	....******
	..**.....*
	**.*.....*
	....*...*.
	......*...
	......**..
	.....****.
	.....**.**
	.......**.
     In December 2015, the Coe ship was discovered in an asymmetric
   random {soup} on {Catagolue}. This was the first time any non-p4 ship
   was discovered in a random asymmetric soup experiment, winning Adam
   P. Goucher a 50-euro prize offered by Ivan Fomichev.

:Coe's p8: (p8)  Found by Tim Coe in August 1997.
	**..........
	**..**......
	.....**.....
	....*..*....
	.......*..**
	.....*.*..**

:Collatz 5N+1 simulator:  An {unknown fate} pattern constructed by David
   Bell in December 2017 that simulates the Collatz 5N+1 algorithm using
   {sliding block memory} and {p1} {technology}, while always having a
   population below 32000.
     The algorithm is simple.  Starting with a number, if it is even
   divide it by 2, otherwise multiply it by 5 and add 1.  When this
   process is iterated a sequence of numbers is generated.  When
   starting with the value of 7, it is currently unknown whether or not
   the sequence ever forms a cycle.
     Because of this the fate of the simulator is also currently
   unknown. It may become stable, or become an oscillator with a high
   period, or have a bounding box which grows irregularly.

:colour:  = {colour of a glider}

:colour-changing:  See {colour of a glider}.  The {reflector} shown in
   {p8 bouncer} is colour-changing, as are its 5/6/7/8 and higher-period
   versions.

:colour-changing semi-Snark:  = {CC semi-Snark}.

:colourised Life:  A {cellular automaton} that is the same as Life
   except for the use of a number of different ON states ("colours").
   All ON states behave the same for the purpose of applying the Life
   rule, but additional rules are used to specify the colour of the
   resulting ON cells.  Examples are {Immigration} and {QuadLife}.

:colour of a glider:  The colour of a {glider} is a property of the
   glider that remains constant while the glider is moving along a
   straight path, but that can be changed when the glider bounces off a
   {reflector}.  It is an important consideration when building
   something using reflectors.
     The colour of a glider can be defined as follows.  First choose
   some cell to be the origin.  This cell is then considered to be
   white, and all other cells to be black or white in a checkerboard
   pattern.  (So the cell with coordinates (m,n) is white if m+n is
   even, and black otherwise.)  Then the colour of a glider is the
   colour of its leading cell when it is in a phase that can be rotated
   to look like this:
	***
	..*
	.*.
     A reflector that does not change the colour of gliders obviously
   cannot be used to move a glider onto a path of different colour than
   it started on.  But a 90-degree reflector that does change the colour
   of gliders is similarly limited, as the colour of the resulting
   glider will depend only on the direction of the glider, no matter how
   many reflectors are used.  For maximum flexibility, therefore, both
   types of reflector are required.
     Small periodic colour-changing glider reflectors ({bouncer}s) are
   known, and also small periodic colour-preserving glider reflectors
   ({bumper}s).  Among stable patterns, only a small colour-preserving
   reflector ({Snark}) is known.  The smallest known 90-degree
   colour-changing reflector is given at the end of the {reflector}
   entry.

:colour-preserving:  See {colour of a glider}.  {Snark}s and {bumper}s
   are colour-preserving reflectors.

:colour-preserving semi-Snark:  = {CP semi-Snark}

:complementary blinker:  = {fore and back}

:component:  A partial {glider synthesis} that can be used in the same
   way in multiple {glider recipe}s.  A component transforms part of an
   object under construction in a well-defined way, without affecting
   the rest of the object.  For example, this well-known component can
   be used to add a {hook} to any object that includes a protruding
   {table} end, converting it to a {long bookend}:
	.......*...................*...................*
	.....**..................**..................**.
	......**..................**..................**
	................................................
	..*...................*...................*.....
	*.*.................*.*.................*.*.....
	.**..*...............**..*...............**..*..
	.....*.*.................*.*.................*.*
	.....**..................**..................**.
	................................................
	................................................
	....................*...........................
	...*..*............*.*.*..*............**..*..*.
	...****.............**.****............*...****.
	......................*.................***.....
	.....**...............*.*.................*.*...
	.....**................*.*.................**...
	........................*.......................
     "Component" is also used to specify any piece of an object -
   {spaceship}, {oscillator}, etc. - that can be combined with other
   components in specific ways according to a {grammar} to produce a
   variety of objects.  The components can either be independent objects
   that only occasionally react with each other, or else they can be
   fused together to support each other.  For example, any
   {branching spaceship} is made up of several components, and there is
   a single repeating component in any {wicktrailer}.

:composite:  See {composite conduit}.

:composite conduit:  A signal-processing {conduit} that can be
   subdivided into two or more {elementary conduit}s.

:compression:  = {repeat time}, {recovery time}.

:computational universality:  See {universal computer}.

:conduit:  Any arrangement of {still life}s and/or {oscillator}s that
   moves an active object to another location, perhaps also transforming
   it into a different active object at the same time, but without
   leaving any permanent debris (except perhaps gliders, or other
   spaceships) and without any of the still lifes or oscillators being
   permanently damaged.  Probably the most important conduit is the
   following remarkable one (Dave Buckingham, July 1996) in which a
   {B-heptomino} is transformed into a {Herschel} in 59 generations.
	.........**.*
	*.**......***
	**.*.......*.
	.............
	.........**..
	.........**..
   Several hundred {elementary conduit}s are now known, with recent
   discoveries primarily made via {search program}s such as {CatForce}
   and {Bellman}.

:conduit 1:  = {BFx59H}.

:confused eaters: (p4)  Found by Dave Buckingham before 1973.
	*..........
	***........
	...*.......
	..*........
	..*..*.....
	.....*.....
	...*.*.....
	...**..**..
	.......*.*.
	.........*.
	.........**

:constellation:  A general term for a group of two or more separate
   objects, usually small still lifes and low-period oscillators.
   Compare {pseudo still life}.

:construction arm:  An adjustable mechanism in a {universal constructor}
   that allows new objects to be constructed in any chosen location that
   the arm can reach.  A construction arm generally consists of a
   {shoulder} containing fixed guns or edge shooters, a movable
   {construction elbow} that slides forward and backward along the
   {construction lane}(s), and in the case of {single-arm} universal
   constructors, a {hand} target object at the construction site that
   can be progressively modified by a {slow salvo} to produce each
   desired object.

:construction elbow:  One of the components of a {construction arm} in a
   {universal constructor}.  The elbow usually consists of a single
   {Spartan} still life or small constellation.  It accepts
   {elbow operation} recipes, in the form of {salvo}s coming from the
   construction arm's {shoulder}.
     These recipes may do one of several things:  1) {pull} the elbow
   closer to the shoulder, 2) {push} the elbow farther from the
   shoulder, 3) emit a glider on a particular output {lane} (while also
   optionally pushing or pulling the elbow); 4) create a "{hand}" target
   block or other useful object as a target for output gliders, to one
   side of the {construction lane}; 5)  duplicate the elbow, or 6)
   destroy the elbow.
     Elbows that receive and emit orthogonally-travelling {spaceship}s
   instead of gliders are technically possible, but no working examples
   are currently known.  The discussion below assumes that gliders are
   used to communicate between the shoulder, elbow, and hand locations.
     If a mechanism can be programmed to generate recipes for at least
   the first three options listed above, it is generally capable of
   functioning as a {universal constructor}.  The main requirement is
   that push and pull {elbow operation}s should be available that are
   either minimal (1{fd}) or the distances should be relatively prime.
     Depending on the {elbow operation} library, there may be only one
   type of elbow, or there may be two or more elbow objects, with
   recipes that convert between them.  The {9hd} library had just one
   elbow type, a block.  The original 10{hd} library had two elbows,
   blocks in mirror-symmetric locations; this was expanded to a larger
   list for the {10hd Demonoid}.  The {0hd Demonoid} also has a
   multi-elbow recipe library.  A {slow elbow} toolkit may make use of
   an even larger number of glider output recipes, because the {target}
   elbow object in that case is not restricted to a single diagonal
   line.
     If only one colour, parity, or phase of glider can be emitted, then
   the mechanism will be limited to producing {monochromatic salvo}s or
   {monoparity salvo}s.  These are less efficient at most construction
   tasks, but are still generally accepted to enable
   {universal toolkit}s.  See also {half-baked knightship}.

:construction envelope:  The region affected by an active reaction, such
   as a {glider synthesis} of an object.  The envelope corresponds to
   the state-2 blue cells in {LifeHistory}.  See also {edgy}.

:construction lane:  Part of a {construction arm} between the {shoulder}
   and the {elbow} - in particular, one of the fixed {lane}s that
   {elbow operation} signals travel on.  All known
   {universal constructor}s have used arms with two or more construction
   lanes, except for the ones in the {0hd Demonoid} and in recent
   {single-channel} construction recipes.

:construction recipe:  One or more streams of {glider}s or other signals
   fed into a {universal constructor} to create a target object.
   Compare {glider recipe}.

:construction universality:  See {universal constructor}.

:converter:  A {conduit} in which the input object is not of the same
   type as the output object.  This term tends to be preferred when
   either the input object or the output object is a {spaceship}.
     The following diagram shows a p8 {pi-heptomino}-to-{HWSS}
   converter.  This was originally found by Dave Buckingham in a larger
   form (using a {figure-8} instead of the {boat}).  The improvement
   shown here is by Bill Gosper (August 1996).  Dieter Leithner has
   since found (much larger) {oscillator}s of periods 44, 46 and 60 that
   can be used instead of the {Kok's galaxy}.
	.*.*..*........
	.***.*.**......
	*......*.....*.
	.*.....**...*.*
	.............**
	**.....*.......
	.*......*......
	**.*.***.......
	..*..*.*.......
	............***
	............*.*
	............*.*
     For another periodic converter, see the glider-to-LWSS example in
   {queen bee shuttle pair}.  However, many converters are {stable}.
   Examples of {elementary conduit} converters include {BFx59H},
   {135-degree MWSS-to-G}, and {45-degree MWSS-to-G}.
     The earliest and simplest stable converters known are shown below.
   These are an HWSS-to-loaf, MWSS-to-beehive, and LWSS-to-blinker.
   These can serve as {memory cell}s, or as the first steps in
   constructing objects using {salvo}s.
	.........................*..............................
	..**...................*...*.................*..*.......
	*....*......................*....................*......
	......*................*....*................*...*......
	*.....*.................*****.................****......
	.******.................................................
	.........**....................**...................**..
	.........*.*...................*....................*...
	...........*....................***..................***
	...........**.....................*....................*

:convoy:  A collection of {spaceship}s all moving in the same direction
   at the same speed.  Convoys are usually not destroyed by the
   reactions that they cause.  Compare {salvo}.  For examples, see
   {reanimation}, {fly-by deletion} and {glider turner}.

:copperhead: (c/10 orthogonally, p10)  The following small c/10
   {spaceship}, discovered by conwaylife.com forum user 'zdr' on 5 March
   2016, using a simple depth-first search program.  A
   {glider synthesis} was found on the same day.
	.****.
	......
	.*..*.
	*.**.*
	*....*
	......
	*....*
	**..**
	******
	.*..*.
	..**..
	..**..
   Later that same month Simon Ekstrom added a {sparky} {tagalong} for
   the copperhead to produce the {fireship}.  This allowed for the
   construction of c/10 puffers and rakes.

:Corder-:  Prefix used for things involving {switch engine}s, after
   Charles Corderman.

:Corder engine:  = {switch engine}

:Cordergun:  A {gun} firing {Cordership}s.  The first was built by Jason
   Summers in July 1999, using a {glider synthesis} by Stephen Silver.

:Cordership:  Any {spaceship} based on {switch engine}s.  These
   necessarily move at a speed of c/12 diagonally with a period of 96 or
   a multiple thereof.  The first Cordership was constructed by Dean
   Hickerson in April 1991, using 13 switch engines.  He soon reduced
   this to 10, and in August 1993 to 7.  In July 1998 he reduced it to
   6.  In January 2004, Paul Tooke found the 3-engine {glide symmetric}
   Cordership shown below.
	................................**.*...........................
	...............................***.*......*.*..................
	..............................*....*.*....*....................
	...............................**......*.*...*.................
	................................*...*..*..**...................
	...................................*.**...*....................
	..................................*.*................**........
	..................................*.*................**........
	...............................................................
	...............................................................
	...............................................................
	...............................................................
	...............................................................
	...............................................................
	.............................................................**
	....................................................**.......**
	.......................................*.........*.****........
	..................................*...*****.....**.*...**......
	.................................*.*.......**....*..**.**......
	.................................*.......*.**.....******.......
	..................................*........**......*...........
	...................................*...****....................
	........................................***....................
	........................*.*.........**.........................
	........................*.*.*......*.*.........................
	.......................*..**.*....**...........................
	........................**...*.*.**.*..........................
	........................**...**.*****..........................
	............................*.**...**..........................
	...........................*.*.................................
	..**.*.........................................................
	.***.*......*.*................................................
	*....*.*....*..................................................
	.**......*.*...*...............................................
	..*...*..*..**...........*.....................................
	.....*.**...*...........***....................................
	....*.*.................*..*...................................
	....*.*................*....*..................................
	........................*......................................
	...............................................................
	........................*..*...................................
	.........................*.*...................................
	...............................................................
	.....................*.........................................
	....................***........................................
	...................**.**.......................................
	.........*........**.*.....*...................................
	....*...*****....**......**....................................
	...*.*.......**..**.......**...................................
	...*.......*.**................................................
	....*........**................................................
	.....*...****..................................................
	..........***..................................................
	...............................................................
	...............................................................
	...............................................................
	...........**..................................................
	...........**..................................................
     At the end of 2017, Aidan F. Pierce discovered a clean
   {2-engine Cordership}.  There is also an adjustable-length 4-engine
   Cordership found by Michael Simkin, made up of two identical or
   mirror-image 2-engine components.  The leading pair of switch engines
   builds a block trail, which are then deleted by the trailing pair.
     Corderships generate {spark}s which can {perturb} other objects in
   many ways, especially gliders which can reach them from the side or
   from behind.  Some perturbations reflect gliders back the way they
   came, and can be used for constructions such as the {caber tosser}
   and the {infinite glider hotel}.

:cousins: (p3)  This contains two copies of the {stillater} {rotor}.
	.....*.**....
	...***.*.*...
	*.*......*...
	**.**.**.*.**
	...*.*....*.*
	...*.*.***...
	....**.*.....

:cover:  The following {induction coil}.  See {scrubber} for an example
   of its use.
	....*
	..***
	.*...
	.*...
	**...

:covered table:  = {cap}

:cow: (c p8 fuse)
	**.......**..**..**..**..**..**..**..**..**..**..**..**.....
	**....*.***..**..**..**..**..**..**..**..**..**..**..**...**
	....**.*.................................................*.*
	....**...*************************************************..
	....**.*..................................................*.
	**....*.***..**..**..**..**..**..**..**..**..**..**..**..**.
	**.......**..**..**..**..**..**..**..**..**..**..**..**.....

:CP pulsar:  = {pulsar}

:CP semi-cenark:  A {colour-preserving} variant of Tanner Jacobi's
   century-based semi-Snark mechanism, the {semi-cenark}.  See
   {CC semi-cenark} for the {colour-changing} version, or {semi-cenark}
   for repeat time details and an alternate initial catalyst.
	.*............**........
	..*..........*.*........
	***.....**..*...........
	........*..*.**.........
	.....*....**.*.*........
	...*.*........*.........
	....**..............**..
	....................*...
	.......**.........*.*...
	.......**.........**....
	........................
	........................
	........................
	....**....**............
	...*.*...*.*............
	...*......*.............
	..**...............**...
	....................*...
	....................*.**
	.................**.**.*
	..................*.....
	................*.*.....
	................**......

:CP semi-Snark:  A period-multiplying {colour-preserving} {signal}
   {conduit} found by Tanner Jacobi in October 2017, producing one
   output {glider} for every two input gliders.  It is made by replacing
   one of the eaters in a {Snark} with a {catalyst} found using
   {Bellman}.  The catalyst causes the formation of a {tub} which
   requires a second glider to delete.  However, this adds 5 ticks to
   the repeat time, so that it becomes 48.  This is still 3 ticks faster
   than the {CC semi-Snark}.
	.*............................
	..*.............**............
	***..............*............
	...............*.....**.......
	...............**.....*.......
	......................*.**....
	...............**..**.*..*....
	...............**...*.**......
	....................*.........
	...................**.........
	..............................
	.........................**...
	.............*............*...
	..............*...........*.**
	............***...**....***..*
	..................**...*...**.
	.......................****...
	.........**...............*...
	........*.*............***....
	........*.............*.......
	.......**..............*****..
	...........................*..
	.........................*....
	.........................**...

:crab:  = {quarter}.

:crane: (c/4 diagonally, p4)  The following {spaceship} found by Nicolay
   Beluchenko in September 2005, a minor modification of a {tubeater}
   found earlier by Hartmut Holzwart.  The wing is of the same form as
   in the {swan} and {Canada goose}.
	.**.................
	**..................
	..*.................
	....**...*..........
	....**..*.*.........
	.......**.*.........
	.......**...........
	.......**...........
	.................**.
	.........*....**.*..
	.........***..**....
	.........***..**....
	..........**........
	....................
	............*.......
	...........**.......
	...........*........
	............*.......
	....................
	.............**.....
	..............*.**..
	..................*.
	...............**...
	...............**...
	.................*..
	..................**

:cross: (p3)  Found by Robert Wainwright in October 1989.  The members
   of this family are all {polyomino}es.

	..****..
	..*..*..
	***..***
	*......*
	*......*
	***..***
	..*..*..
	..****..
   In February 1993, Hartmut Holzwart noticed that this is merely the
   smallest of an infinite family of p3 oscillators.  The next smallest
   member is shown below.
	..****.****..
	..*..*.*..*..
	***..***..***
	*...........*
	*...........*
	***.......***
	..*.......*..
	***.......***
	*...........*
	*...........*
	***..***..***
	..*..*.*..*..
	..****.****..

:crowd: (p3)  Found by Dave Buckingham in January 1973.
	...........*..
	.........***..
	.....**.*.....
	.....*...*....
	.......**.*...
	...****...*...
	*.*.....*.*.**
	**.*.*.....*.*
	...*...****...
	...*.**.......
	....*...*.....
	.....*.**.....
	..***.........
	..*...........

:crown:  The p12 part of the following p12 {oscillator}, where it is
   {hassle}d by a {caterer}, a {jam} and a {HW emulator}.  This
   oscillator was found by Noam Elkies in January 1995.
	..........*...........
	..........*......*....
	...*....*...*...**....
	...**....***..........
	.........***..***..*.*
	.*..***.........*.****
	*.*.*...............**
	*..*..................
	.**........**.........
	......**.*....*.**....
	......*..........*....
	.......**......**.....
	....***..******..***..
	....*..*........*..*..
	.....**..........**...

:crucible:  = {cauldron}

:crystal:  A regular growth that is sometimes formed when a stream of
   {glider}s, or other {spaceship}s, is fired into some junk.
     The most common example is initiated by the following collision of
   a glider with a {block}.  With a glider stream of even {period} at
   least 82, this gives a crystal which forms a pair of {beehive}s for
   every 11 gliders which hit it.
	.*......
	..*...**
	***...**

:C-to-G:  = {century-to-glider converter}

:cuphook: (p3)  Found by Rich Schroeppel, October 1970.  This is one of
   only three essentially different p3 {oscillator}s with only three
   cells in the {rotor}.  The others are {1-2-3} and {stillater}.
	....**...
	**.*.*...
	**.*.....
	...*.....
	...*..*..
	....**.*.
	.......*.
	.......**
   The above is the original form, but it can be made more compact:
	....**.
	...*.*.
	...*...
	**.*...
	**.*..*
	...*.**
	...*...
	..**...

:curl:  = {loop}

:dart: (c/3 orthogonally, p3)  Found by David Bell, May 1992.  A
   25-glider recipe for the dart was found in December 2014 by Martin
   Grant and Chris Cain, making it the first glider-constructible c/3
   spaceship.
	.......*.......
	......*.*......
	.....*...*.....
	......***......
	...............
	....**...**....
	..*...*.*...*..
	.**...*.*...**.
	*.....*.*.....*
	.*.**.*.*.**.*.

:dead spark coil: (p1)  Compare {spark coil}.
	**...**
	*.*.*.*
	..*.*..
	*.*.*.*
	**...**

:debris:  = {ash}.

:de Bruijn diagram:  = {de Bruijn graph}

:de Bruijn graph:  As applied to Life, a de Bruijn graph is a graph
   showing which pieces can be linked to which other pieces to form a
   valid part of a Life pattern of a particular kind.
     For example, if we are interested in {still life}s, then we could
   consider 2x3 rectangular pieces and the de Bruijn graph would show
   which pairs of these can be overlapped to form 3x3 squares in which
   the centre cell remains unchanged in the next generation.
     David Eppstein's {search program} {gfind} is based on de Bruijn
   graphs.

:Deep Cell:  A pattern by Jared James Prince, based on David Bell's
   {unit Life cell}, in which each unit cell simulates two Life cells,
   in such a way that a Life universe filled with Deep Cells simulates
   two independent Life universes running in parallel.
     In fact, a Life universe filled with Deep Cells can simulate
   infinitely many Life universes, as follows.  Let P_1, P_2, P_3, ...
   be a sequence of Life patterns.  Set the Deep Cells to run a
   simulation of P_1 in parallel with a simulation of a universe filled
   with Deep Cells, with these simulated Deep Cells running a simulation
   of P_2 in parallel with another simulation of a universe filled with
   Deep Cells, with these doubly simulated Deep Cells simulating P_3 in
   parallel with yet another universe of Deep Cells, and so on.
     Deep Cell is available from {http://psychoticdeath.com/life.htm}.

:Demonoid:  The first {self-constructing} diagonal spaceship. A 0{hd}
   Demonoid was completed by Chris Cain in December 2015, shortly after
   a much larger 10hd version was constructed the previous month in
   collaboration with Dave Greene. The 0hd spaceship fits in a bounding
   box about 55,000 cells square, and displaces itself by 65 cells
   diagonally every 438,852 generations.
     The first 0hd Demonoid was fired by a {gun}.  No spaceship gun
   pattern had previously been completed before the first appearance of
   the actual spaceship.
     In June 2017 Dave Greene completed a much simpler {single-channel}
   Demonoid using a temporary {lossless elbow}, which displaces itself
   79 cells diagonally every 1,183,842 ticks.  This was an improvement
   in terms of design complexity, but not in terms of speed, population,
   or bounding box.  However, all of these could be further optimized.
   A smaller Hashlife-friendly single-channel Demonoid design was
   completed in 2018.

:demultiplexer:  A simple {Herschel} {circuit} consisting of three
   {eater1}s, found by Brice Due in August 2006.  An input Herschel
   places a boat in a location accessible to an input glider.  If the
   boat is present, a {one-time} {turner} reaction occurs and the glider
   is turned 90 degrees onto a new lane.
	...........................*.....
	........**.................*.*...
	.........*.................**....
	.........*.*.....................
	..........**.....................
	.......................**........
	.......................*.*.......
	........................*........
	.................................
	.................................
	.............................**..
	..........*..................*.*.
	..........*.*..................*.
	..........***............**....**
	............*............*.*.....
	...........................*.....
	...........................**....
	.................................
	.................................
	..**.............................
	.*.*.............................
	.*...............................
	**...............................
   If the Herschel and boat are removed from the above pattern, the
   glider passes cleanly through the circuit.  It can be used as the "0"
   output of a one-bit {memory cell}, where the 90-degree output would
   be the "1" output.  This was the method used to store presence or
   absence of neighbor {metacell}s in the {p1 megacell}.

:demuxer:  = {demultiplexer}

:density:  The density of a pattern is the limit of the proportion of
   live cells in a (2n+1)x(2n+1) square centred on a particular cell as
   n tends to infinity, when this limit exists.  (Note that it does not
   make any difference what cell is chosen as the centre cell.  Also
   note that if the pattern is finite then the density is zero.)  There
   are other definitions of density, but this one will do here.
     In 1994 Noam Elkies proved that the maximum density of a stable
   pattern is 1/2, which had been the conjectured value.  See the paper
   listed in the bibliography.  Marcus Moore provided a simpler proof in
   1995, and in fact proves that a {still life} with an m x n
   {bounding box} has at most (mn+m+n)/2 cells.
     But what is the maximum average density of an oscillating pattern?
   The answer is conjectured to be 1/2 again, but this remains unproved.
   The best upper bound so far obtained is 8/13 (Hartmut Holzwart,
   September 1992).
     The maximum possible density for a {phase} of an oscillating
   pattern is also unknown.  An example with a density of 3/4 is known
   (see {agar}), but densities arbitrarily close to 1 may perhaps be
   possible.

:dependent conduit:  A {Herschel conduit} in which the input {Herschel}
   interacts with catalysts in the first few ticks.  The standard
   interaction actually starts at T=-3, before the Herschel is
   completely formed.  Compare {independent conduit}.  The Herschel is
   prevented from emitting its {first natural glider}.  This is useful
   in cases where the previous conduit cannot survive a first natural
   glider emitted from its output Herschel.
     This term is somewhat confusing, since it is actually the previous
   conduit that depends on the dependent conduit to suppress the
   problematic glider.  Dependent conduits such as the {F166} and
   {Lx200} do not actually depend on anything.  They can be freely
   connected to any other conduits that fit, as long as the output
   Herschel evolves from its standard great-grandparent.  As of this
   writing, the {Fx158} is the only known case where a conduit's output
   Herschel has an alternate great-grandparent, which is incompatible
   with dependent conduits' initial transparent block.

:destructive read:  The most common type of test reaction in
   {memory cell} circuitry.  Information is stored in a memory cell by
   placing objects in known positions, or by changing the state of a
   stable or periodic {toggle circuit}.  A destructive-read test
   consists of sending one or more {signal}s to the memory cell.  A
   distinct output signal is produced for each possible state of the
   memory cell, which is reset to a known "zero" or "rest" state.  See
   for example {boat-bit}, {keeper}, and {demultiplexer}.
     To permanently store information in a destructive-read memory cell,
   the output signal(s) must be used, in part, to send appropriate
   signals back to the memory cell to restore its state to its previous
   value.  With output looped back to input, this larger composite
   circuit then effectively becomes a {non-destructive read} memory
   cell.

:destructor arm:  A dedicated {construction arm} in the {Gemini}
   spaceship, used only for removing previously active {circuit}ry once
   it is no longer needed.  More generally, any circuitry in a
   self-constructing pattern dedicated exclusively to cleanup.

:D-heptomino:  = {Herschel}

:diamond:  = {tub}

:diamond ring: (p3)  Found by Dave Buckingham in 1972.
	......*......
	.....*.*.....
	....*.*.*....
	....*...*....
	..**..*..**..
	.*....*....*.
	*.*.**.**.*.*
	.*....*....*.
	..**..*..**..
	....*...*....
	....*.*.*....
	.....*.*.....
	......*......

:diehard:  Any pattern that vanishes, but only after a long time.  The
   following example vanishes in 130 generations, which is probably the
   limit for patterns of 7 or fewer cells.  Note that there is no limit
   for higher numbers of cells.  E.g., for 8 cells we could have a
   glider heading towards an arbitrarily distant blinker.
	......*.
	**......
	.*...***

:dinner table: (p12)  Found by Robert Wainwright in 1972.
	.*...........
	.***.......**
	....*......*.
	...**....*.*.
	.........**..
	.............
	.....***.....
	.....***.....
	..**.........
	.*.*....**...
	.*......*....
	**.......***.
	...........*.

:dirty:  Opposite of {clean}.  A reaction which produces a large amount
   of complicated junk which is difficult to control or use is said to
   be dirty.  Many basic {puffer engine}s are dirty and need to be
   {tame}d by accompanying {spaceship}s in order to produce clean
   output.  Similarly, a dirty {conduit} is one that does not recover
   perfectly after the passage of a {signal}; one or more extra {ash}
   objects are left behind (or more rarely a {catalyst} is damaged) and
   additional signals must be used to clean up the circuit before it can
   be re-used.

:diuresis: (p90)  Found by David Eppstein in October 1998.  His original
   stabilization used {pentadecathlon}s.  The stabilization with
   complicated {still life}s shown here (in two slightly different
   forms) was found by Dean Hickerson the following day.  The name is
   due to Bill Gosper (see {kidney}).
	.....**................**....
	......*................*.....
	......*.*............*.*.....
	.......**............**......
	.............................
	....**..................**...
	....*.*..........**....*.*...
	.....*..........*.*.....*....
	..*.............**.........*.
	..******........*.....******.
	.......*..............*......
	....**..................**...
	....*....................*...
	.....*..................*....
	..***..*..............*..***.
	..*..***........*.....***...*
	...*............**.......***.
	....**..........*.*.....*....
	......*..........**....*..**.
	....**..................**.*.
	.*..*....................*...
	*.*.*..**............**..*...
	.*..*.*.*............*.*.**..
	....*.*................*..*..
	.....**................**....

:dock:  The following {induction coil}.
	.****.
	*....*
	**..**

:domino:  The 2-cell {polyomino}.  A number of objects, such as the
   {HWSS} and {pentadecathlon}, produce domino {spark}s.

:dormant:  An object that is either stable or oscillates without
   producing any output, until it is {trigger}ed by an appropriate
   signal, which then produces some desired action.  For example,
   {freeze-dried} objects are dormant until the arrival of a particular
   glider.

:do-see-do:  The following reaction, found by David Bell in 1996, in
   which two {glider}s appear to circle around each other as they are
   reflected 90 degrees by a {twin bees shuttle}.  Four copies of the
   reaction can be used to create a p92 glider loop which repeats the
   do-see-do reaction forever.
	.....................................................*.*
	.....................................................**.
	......................................................*.
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	................................................**......
	................................................*.......
	..............................................*.*.......
	..............................................**........
	..............................*.*.......................
	..............................**........................
	...............................*........................
	........................................................
	.......................***..............................
	**........***........**.*.**............................
	**........*...*.....*.....**............................
	..........*....*.....**.*.**............................
	...........*...*.......***..............................
	........................................................
	...........*...*........................................
	..........*....*........................................
	**........*...*............**...........................
	**........***..............**...........................

:double-barrelled:  Of a {gun}, emitting two streams of {spaceship}s (or
   {rake}s) every period.  For examples, see {B-52 bomber},
   {Simkin glider gun}, and {p246 gun}.  In most cases, the two streams
   are alternately emitted 1/2 period apart.  It is also possible for
   the two streams to be emitted simultaneously, as in this
   double-barrelled glider gun by Bill Gosper:
	.................*................................
	.................**...............................
	..................**..............................
	.................**...............................
	................................*.................
	...............................**...............**
	..............................**................**
	.................**............**.................
	**................**..............................
	**...............**...............................
	.................*................................
	...............................**.................
	..............................**..................
	...............................**.................
	................................*.................

:double block reaction:  A certain reaction that can be used to
   stabilize the {twin bees shuttle} (qv).  This was discovered by David
   Bell in October 1996.
     The same reaction sometimes works in other situations, as shown in
   the following diagram where a pair of blocks eats an {R-pentomino}
   and a {LWSS}.  (The LWSS version was known at least as early 1994,
   when Paul Callahan saw it form spontaneously as a result of firing an
   LWSS stream at some random junk.)
	.****.....**....
	*...*......**.**
	....*......*..**
	*..*............
	................
	.............**.
	.............**.

:double caterer: (p3)  Found by Dean Hickerson, October 1989.  Compare
   {caterer} and {triple caterer}.
	.....**...*........
	....*..*..***......
	....**.*.....*.....
	......*.****.*.....
	..***.*.*...*.**...
	.*..*..*...*..*.*..
	*.*..*...*.**....*.
	.*..........**.***.
	..**.**.**...*.....
	...*...*.....*.***.
	...*...*......**..*
	.................**

:double ewe: (p3)  Found by Robert Wainwright before September 1971.
	......**............
	.......*............
	......*.............
	......**............
	.........**.........
	......***.*.........
	*.**.*..............
	**.*.*..............
	.....*...*..........
	....*...**....**....
	....**....**...*....
	..........*...*.....
	..............*.*.**
	..............*.**.*
	.........*.***......
	.........**.........
	............**......
	.............*......
	............*.......
	............**......

:double wing:  = {moose antlers}.  This term is no longer in use.

:dove:  The following {induction coil}, found in 2015 to be a possible
   active reaction for the input or output of a {converter}.
	.**..
	*..*.
	.*..*
	..***

:down boat with tail:  = {cis-boat with tail}

:dr:  Short identifier for Dean Hickerson's 'drifter' search program,
   used at various times to find {wire}s, {eater}s, higher-period
   {billiard table configuration}s, and related {signal}-carrying and
   signal-processing mechanisms.  See also {drifter}.

:dragon: (c/6 orthogonally, p6)  This {spaceship}, discovered by Paul
   Tooke in April 2000, was the first known {c/6 spaceship}.  With 102
   cells, it was the smallest known orthogonal c/6 spaceship until
   Hartmut Holzwart discovered {56P6H1V0} in April 2009.
	.............*..**......*..***
	.....*...****.******....*..***
	.*****....*....*....***.......
	*......**.*......**.***..*.***
	.*****.***........****...*.***
	.....*..*..............*......
	........**..........**.**.....
	........**..........**.**.....
	.....*..*..............*......
	.*****.***........****...*.***
	*......**.*......**.***..*.***
	.*****....*....*....***.......
	.....*...****.******....*..***
	.............*..**......*..***

:drain trap:  = {paperclip}.  This term is no longer in use.

:D read:  = {destructive read}

:dried:  = {freeze-dried}.

:drifter:  A perturbation moving within a stable pattern.  Dean
   Hickerson has written a {search program} to search for drifters, with
   the hope of finding one which could be moved around a track.  Because
   drifters can be very small, they could be packed more tightly than
   {Herschel}s, and so allow the creation of {oscillator}s of periods
   not yet attained, and possibly prove that Life is {omniperiodic}.
   Hickerson has found a number of components towards this end, but it
   has proved difficult to change the direction of movement of a
   drifter, and so far no complete track has been found.  However,
   Hickerson has had success using the same program to find {eater}s
   with novel properties, such as {sparking eater}s and the ones shown
   in {diuresis}.

:dual 1-2-3-4:  = {Achim's p4}

:duoplet:  A diagonal two-bit spark produced by many oscillators and
   eater reactions.  Among other uses, it can reflect gliders 90
   degrees.  The following pattern shows an {eater5} eating gliders and
   producing duoplets which are then used to reflect a separate glider
   stream.  If only one glider is present, the eater5 successfully
   absorbs it, so this mechanism may be considered to be a simple AND
   gate.
	..*....................
	*.*....................
	.**....................
	.......................
	.......................
	.......*...............
	.....*.*...............
	......**...............
	.....................*.
	....................*..
	....................***
	.......................
	.......................
	................*......
	...............*.......
	...............***.....
	.......................
	....................**.
	................*...**.
	...............*.*.....
	..............*.*......
	..............*........
	.............**........

:dying spark:  See {spark}.  A spark by definition dies out completely
   after some number of ticks.

:early universe:  Conway's somewhat confusing term for {sparse Life}.

:eater:  Any {still life} that has the ability to interact with certain
   patterns without suffering any permanent damage.  (If it doesn't
   suffer even temporary damage then it may be referred to as a {rock}.)
   The {eater1} is a very common eater, and the term "eater" is often
   used specifically for this object.  Other eaters include {eater2},
   {eater3}, {eater4}, and {eater5}, and many hundreds of others are
   known.  Below is a complex eater found by Dean Hickerson in 1998
   using his {dr} {search program}.  It takes 25 {tick}s to recover
   after feasting on a glider:
	.*.............
	..*............
	***............
	......**.**.*..
	.......*.*.**..
	.......*.*.....
	........**.....
	**.............
	*..*.**........
	..**.*.........
	...*.*.....**.*
	..*..***...*.**
	...**...*......
	.....****......
	.....*.........
	...*.*.**......
	...**..*.......
	.......*.*.....
	........**.....
     Some common {still life}s can act as eaters in some situations,
   such as the {block}, {ship}, and {tub}.  In fact the block was the
   first known eater, being found capable of eating beehives from a
   {queen bee}.

:eater1: (p1)  Usually simply called an {eater}, and also called a
   fishhook.
	**..
	*...
	.***
	...*
     This eater can be constructed using a simple two-glider collision,
   as shown in {stamp collection}.  It is often modified in various
   ways, or {weld}ed to other objects, to allow tighter packing of
   {circuit}s or to allow a {signal} {stream} to pass close by.  See
   {clearance} for an eater1 variant that is 1{hd} shorter to the
   southeast than the standard fishhook form.  An eater1 can also be
   used as a 90-degree {one-time} {turner}.
     Its ability to eat various objects was discovered by Bill Gosper in
   1971.  The fishhook eater can consume a glider, a {LWSS}, and a
   {MWSS} as shown below.  It is not able to consume an {HWSS}, however.
   See {honey bit} or {killer toads} for that.
	...........................**
	...........................*.
	..*......................*.*.
	*...*.........*..........**..
	.....*.........*.............
	*....*.....*...*.....***.....
	.*****......****.......*.....
	......................*......

:eater2: (p1)  This {eater} was found by Dave Buckingham in the 1970s.
   Mostly it works like the ordinary {eater1} but with two slight
   differences that make it useful despite its size: it takes longer to
   recover from each bite, and it can eat objects appearing at two
   different positions.
	**.*...
	**.***.
	......*
	**.***.
	.*.*...
	.*.*...
	..*....
   The first property means that, among other things, it can eat a
   {glider} in a position that would destroy an {eater1}.  This novel
   glider-eating action is occasionally of use in itself, and combined
   with the symmetry means that an eater2 can eat gliders travelling
   along four adjacent glider {lane}s, as shown below.
     The following eater2 variant (Stephen Silver, May 1998) can be
   useful for obtaining smaller {bounding box}es.  A more compact
   variant with the same purpose can be seen under {gliderless}.
	.*.................
	..*................
	***................
	...................
	....*..............
	.....*.............
	...***.............
	...................
	.......*...........
	........*..........
	......***..........
	...................
	..........*........
	...........*.....**
	.........***......*
	.............**.*..
	.............**.**.
	...................
	.............**.**.
	..............*.*..
	..............*.*..
	...............*...

:eater3: (p1)  This large symmetric {eater}, found by Dave Buckingham,
   has a very different eating action from the {eater1} and {eater2}.
   The {loaf} can take bites out things, being flipped over in the
   process.  The rest of the object merely flips it back again.
	.........**.
	....**..*..*
	.*..*....*.*
	*.*.*.....*.
	.*..*.**....
	....*..*....
	.....*....*.
	......*****.
	............
	........*...
	.......*.*..
	........*...

:eater4: (p1)  Another {eater} by Dave Buckingham, which he found in
   1971, but did not recognize as an eater until 1975 or 1976.  It can't
   eat {glider}s, but it can be used for various other purposes. The
   four NE-most centre cells regrow in a few generations after being
   destroyed by taking a bite out of something, such as suppressing half
   of a developing {traffic light} as it does in the
   {p29 pentadecathlon hassler}.
	...**.........
	...*..........
	**.*..........
	*..**.........
	.**....*......
	...*****......
	...*....**....
	....**..*.....
	......*.*.....
	......*.*.*..*
	.......**.****
	.........*....
	.........*.*..
	..........**..

:eater5: (p1)  A compound {eater} that can eat {glider}s coming from two
   different directions. Also called the tub-with-tail eater (TWIT), it
   is often placed along the edges of glider {lane}s to suppress
   unwanted gliders in {conduit}s. Below is the standard form, a compact
   form with a {long hook}, and an often-useful conjoined form found
   with {Bellman}.  The {sidesnagger} is a Spartan constellation that
   has a similar glider-absorbing function, using a {loaf}.  See also
   {7x9 eater}.
	.*.........*.........*...........
	..*.........*.........*..........
	***.......***.......***..........
	.................................
	......*.........*.........*......
	.....*.........*.........*.......
	.....***.......***.......***.....
	.................................
	..........**.....................
	......*...**....*...**....*...**.
	.....*.*.......*.*...*...*.*...*.
	....*.*.......*.*...*....**...*..
	....*.........*....*.........*...
	...**........**.....***..*****.*.
	......................*..*....*.*
	...........................*..*.*
	..........................**...*.
     With gliders from either direction, the eater5's eating reaction
   creates a {spark} that can be used to reflect other gliders.  See the
   example pattern in {duoplet}, or advance any of the topmost three
   gliders in the above pattern by two {tick}s.

:eater/block frob: (p4)  Found by Dave Buckingham in 1976 or earlier.
	.**.......
	..*.......
	..*.*.....
	...*.*....
	.....**.**
	........**
	..**......
	...*......
	***.......
	*.........

:eater-bound pond:  = {biting off more than they can chew}

:eater-bound Z-hexomino:  = {pentoad}

:eater eating eater:  = {two eaters}

:eater plug: (p2)  Found by Robert Wainwright, February 1973.
	.......*
	.....***
	....*...
	.....*..
	..*..*..
	.*.**...
	.*......
	**......

:eaters plus:  = {French kiss}

:ecologist: (c/2 orthogonally, p20)  This consists of the classic
   {puffer train} with a {LWSS} added to suppress the debris.  See also
   {space rake}.
	****.....**........
	*...*...**.**......
	*........****......
	.*..*.....**.......
	...................
	.....*.........**..
	...***........*****
	..*...*.....*....**
	..*....*****.....**
	..**.*.****....**..
	....*...**.***.....
	.....*.*...........
	...................
	...................
	****...............
	*...*..............
	*..................
	.*..*..............

:edge-repair spaceship:  A {spaceship} which has an edge that possesses
   no {spark} and yet is able to {perturb} things because of its ability
   to repair certain types of damage to itself.  The most useful
   examples are the following two small p3 {c/3 spaceship}s:
	..................................*.....
	........*.......................***.***.
	.......****....................**......*
	..*...*...**.**...........*...*..*...**.
	.****.....*..**..........****...........
	*...*.......*..*........*...*...........
	.*.*..*..................*.*..*.........
	.....*.......................*..........
   These were found by David Bell in 1992, but the usefulness of the
   edge-repair property wasn't recognised until July 1997.  The
   following diagram (showing an edge-repair spaceship deleting a
   {Herschel}) demonstrates the self-repairing action.
	................*.......
	*..............****.....
	*.*.......*...*...**.**.
	***......****.....*..**.
	..*.....*...*.......*..*
	.........*.*..*.........
	.............*..........
   In October 2000, David Bell found that a {T-tetromino} component of a
   {c/4 spaceship} can also be self-repairing.  Stephen Silver noticed
   that it could be used to delete beehives and, in November 2000, found
   the smallest known c/4 spaceship with this edge-repair component - in
   fact, two copies of the component:
	.**..........................
	*..*.........................
	.**..........................
	.............................
	.......*.*...................
	.......*.....................
	.......*.*..*..*.............
	..........*..................
	...........*.**.*............
	............***.*............
	...........*....*..*.**......
	........*...**...*.****......
	........**..*..*.**....*....*
	........*........**....*..***
	.............**...**...*..**.
	.**..........................
	*..*.........................
	.**..........................

:edge shooter:  A {gun} or {signal} {circuit} that fires its gliders (or
   whatever) right at the edge of the pattern, so that it can be used to
   fire them closely parallel to others.  This is useful for
   constructing complex guns.  Compare {glider pusher}, which can in
   fact be used for making edge shooters.
     The following diagram shows a p46 edge shooter found by Paul
   Callahan in June 1994.
	**............**..*....**..**.............
	**............*.**......**.**.............
	...............*......*.*.................
	...............***....**..................
	..........................................
	...............***....**..................
	...............*......*.*.................
	**............*.**......**................
	**............**..*....**.................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	...............................***...***..
	..............................*...*.*...*.
	.............................*...**.**...*
	.............................*.**.....**.*
	...............................*.......*..
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	...............................**.....**..
	...............................**.....**..
     Stable edge shooters became possible with the development of
   {Herschel circuit}ry.  For example, {NW31}, {BNE14T30}, {RNE-19T84},
   and the high-{clearance} {Fx119 inserter} are often used in
   {shotgun}s for complex salvos.  Composite edge-shooter circuits with
   arbitrarily high clearance can be constructed.

:edge spark:  A {spark} at the side of a {spaceship} that can be used to
   {perturb} things as the spaceship passes by.

:edge sparker:  A {spaceship} that produces one or more {edge spark}s.

:edgy:  In {slow salvo} terminology, an edgy glider construction recipe
   is one that places its final product at or very near the edge of its
   {construction envelope}.  Similarly, an edgy {factory} will place its
   output object in an accessible location near the edge of its
   {reaction envelope}.

:egg:  = {non-spark}.  This term is no longer in use.

:E-heptomino:  Name given by Conway to the following {heptomino}.
	.***
	**..
	.**.

:elbow:  Depending on context, this term may refer to a {signal elbow}
   or a {construction elbow}.  See also {elbow ladder}.

:elbow ladder:  Scot Ellison's name for the type of pattern he created
   in which one or more {glider}s shuttle back and forth (using the
   {kickback reaction}) deleting the output gliders from a pair of
   {slide gun}s.

:elbow operation:  A recipe, usually a {salvo} of {glider}s travelling
   on one or more {construction lane}s, that collides with an {elbow}
   {constellation} and performs one of the standard transformations on
   it:  {push}, {pull}, or {fire} for simple construction arms, along
   with possible construct, duplicate-elbow, or delete-elbow ops for
   more complicated systems.  See {construction elbow}.

:electric fence: (p5)  A stabilization of {ants}.  Dean Hickerson,
   February 1993.
	..........*..................................................
	.........*.*........................**.......................
	..*....***.*.....*...................*...*..*......*.....**..
	.*.*..*....**...*.*..................*.***..***...*.*....*...
	.*.*..*.**.......*....................*...**...*.*..*......*.
	**.**.*.*.*****.....*..................**...*..*.*.**.**..**.
	.*.*..*...*..*..*.......**...**...**....**.**..*.*..*.*.*....
	.*..**....**......***.**...**...**...***.....****.***.*...**.
	..*..***..*..*.****...**...**...**...***.**..*....*.*....*..*
	...**...*.*..*.....**...**...**...**......*............*...**
	.....**.*.**.*.**..*......................*........**.*......
	.....*.**.*..*.**....*.................**.*.*................
	...........**.......**..................*..**................
	......................................*.*....................
	......................................**.....................

:elementary:  Not reducible to a combination of smaller parts.
   Elementary {spaceship}s in particular are usually those found by
   search programs, and they can't be subdivided into smaller
   spaceships, tagalongs, and supporting reactions, as contrasted with
   engineered {macro-spaceship}s.

:elementary conduit:  A {conduit} with no recognizable active signal
   stage besides its input and output.  An early example still very
   commonly used is Buckingham's {BFx59H}, which transforms a
   {B-heptomino} into an inverted {Herschel} in 59 ticks.  The BFx59H
   elementary conduit is a component in many of the original {universal}
   {toolkit} of Herschel conduits.  An extension of the same naming
   convention is used for elementary conduits, with the first and last
   letters of the name specifying the input and output {signal} objects.
   As with Herschels, an arbitrary orientation and center point is
   chosen for each object.  "Fx" means the signal moves forward and
   produces a mirror-image output.  See {Herschel conduit} for further
   details.
     Theoretically an elementary conduit may become a composite conduit,
   if another conduit can be found that shares the beginning or end of
   the conduit in question.  In practice this happens only rarely,
   because many of the most likely branch points have already been
   identified: {glider} (G), {LWSS} (L) or {MWSS} (M), {Herschel} (H),
   {B-heptomino} (B), {R-pentomino} (R), {pi-heptomino} (P),
   {queen bee shuttle} (Q), {century} or {bookend} (C), {dove} (D), and
   {wing} (W).  A {Herschel descendant} might qualify, due to the
   elementary conduit that can be seen in the {p184 gun}.  However,
   there are very few simple conduits that produce Herschel descendants
   without Herschels, so in practice this is not a useful branch point.

:elevener: (p1)
	**....
	*.*...
	..*...
	..***.
	.....*
	....**

:Elkies' p5: (p5)  Found by Noam Elkies in 1997.
	.*.......
	*..***...
	..*......
	...*.*..*
	..**.****
	....*....
	....*.*..
	.....**..

:emu:  Dave Buckingham's term for a {Herschel loop} that does not emit
   {glider}s (and so is "flightless").  All known Herschel loops of
   periods 52, 57, 58, 59 and 61 are emus.  See also {Quetzal}.

:emulator:  Any one of three p4 oscillators that produce {spark}s
   similar to those produced by {LWSS}, {MWSS} and {HWSS}.  See
   {LW emulator}, {MW emulator} and {HW emulator}.  Larger emulators are
   also possible, but they require stabilizing objects to suppress their
   {non-spark}s and so are of little use.  The emulators were discovered
   by Robert Wainwright in June 1980.

:engine:  The active portion of an object (usually a {puffer} or {gun})
   which is considered to actually produce its output, and which
   generally permits no variation in how it works.  The other parts of
   the object are just there to support the engine.  For examples, see
   {puffer train}, {Schick engine}, {blinker puffer}, {frothing puffer}
   and {line puffer}.

:engineless:  A {rake} or {puffer} which does not contain a specific
   {engine} for its operation.  Instead it depends on perturbations of
   gliders or other objects by passing spaceships.  The period of such
   objects is often adjustable, and in some cases the speed as well.  An
   early example was the creation of c/5 rakes in September 1997, using
   gliders circulating among a convoy of c/5 spaceships.  More recently,
   the passing spaceships themselves are also constructed, as in the
   {Caterloopillar}.

:en retard: (p3)  Found by Dave Buckingham, August 1972.
	.....*.....
	....*.*....
	**.*.*.*.**
	.*.*...*.*.
	*..*.*.*..*
	.**.....**.
	...**.**...
	...*.*.*...
	....*.*....
	..*.*.*.*..
	..**...**..

:Enterprise: (c/4 diagonally, p4)  Found by Dean Hickerson, March 1993.
	.......***...........
	.....*.**............
	....****.............
	...**.....*..........
	..***..*.*.*.........
	.**...*.*..*.........
	.*.*.*****...........
	**.*.*...*...........
	*........**..........
	.**..*...*.*.........
	....**..*.**......*..
	...........**.....***
	............*..***..*
	............*..*..**.
	.............*.**....
	............**.......
	............**.......
	...........*.........
	............*.*......
	...........*..*......
	.............*.......

:envelope:  See {construction envelope}, {reaction envelope}.

:Eureka: (p30)   A {pre-pulsar} {shuttle} found by Dave Buckingham in
   August 1980.  A variant is obtained by shifting the top half two
   spaces to either side.
	.*..............*.
	*.*....*.......*.*
	.*...**.**......*.
	.......*..........
	..................
	..................
	..................
	.......*..........
	.*...**.**......*.
	*.*....*.......*.*
	.*..............*.

:evolution:  The process or result of running one or more generations of
   an object.  For example, a row of 10 cells evolves into a
   {pentadecathlon}.

:evolutionary factor:  For an unstable pattern, the time to
   stabilization divided by the initial {population}.  For example, the
   {R-pentomino} has an evolutionary factor of 220.6, while {bunnies}
   has an evolutionary factor of 1925.777...  The term is no longer in
   use.

:exhaust:  The debris or {smoke} left behind by a {puffer}, especially
   if the debris is {dirty} and takes many {generation}s to settle.  The
   term is not usually used for the objects created by {clean} puffers.

:exponential filter:  A {toolkit} developed by Gabriel Nivasch in 2006,
   enabling the construction of patterns with asymptotic population
   growth matching O((log log ... log(t))) for any number of nested log
   operations.  See also {quadratic filter}, {recursive filter}.

:exposure:  = {underpopulation}

:extensible:  A pattern is said to be extensible if arbitrarily large
   patterns of the same type can be made by repeating parts of the
   original pattern in a regular way.  For examples, see {p6 shuttle},
   {pentoad}, {pufferfish spaceship}, {snacker}, {wavestretcher},
   {wicktrailer} and {branching spaceship}.

:extra extra long:  = {long^4}

:extra long:  = {long^3}

:extremely impressive: (p6)  Found by Dave Buckingham, August 1976.
	....**......
	...*.***....
	...*....*...
	**.*...**...
	**.*.....**.
	....*****..*
	..........**
	......*.....
	.....*.*....
	......*.....

:extruder:  See {traffic lights extruder}.  A {single-channel}
   constructor arm has also been programmed to extrude a growing {wick}
   consisting of a chain of {Snark}s, again working from the stationary
   {fencepost} end of the wick with no need for a {wickstretcher}
   component.

:F116:  An {elementary conduit}, one of the original sixteen
   {Herschel conduit}s, discovered by Paul Callahan in February 1997.
   After 116 ticks, it produces a {Herschel} at (32, 1) relative to the
   input.  Its {recovery time} is 138 ticks; this can be reduced to 120
   ticks by adding extra mechanisms to suppress the internal glider.  It
   is {Spartan} only if the following conduit is a {dependent conduit},
   so that the {weld}ed {FNG} eater can be removed.  A {ghost Herschel}
   in the pattern below marks the output location:
	........*..........................
	........***........................
	...........*.......................
	..........**.......................
	...................................
	...................................
	...................................
	...................................
	...................................
	...................................
	...................................
	...................................
	...................................
	...................................
	*..................................
	*.*.............................*..
	***.............................*..
	..*.............................***
	..................................*
	...................................
	...................................
	...................................
	...................................
	.........................**........
	...................**.....*........
	...................*.*.***.........
	............**.......*.*...........
	............**.......**............

:F117:  A {composite conduit}, one of the original sixteen
   {Herschel conduit}s, discovered by Dave Buckingham in July 1996.  It
   is made up of two {elementary conduit}s, {HFx58B} + {BFx59H}.  After
   117 ticks, it produces a {Herschel} at (40, -6) relative to the
   input.  Its {recovery time} is 63 ticks.  It can be made {Spartan} by
   replacing the {snake} with an {eater1} in one of two orientations.  A
   {ghost Herschel} in the pattern below marks the output location:
	......................**.....................
	.......................*.....................
	..........*...........*......................
	..........***.........**.....................
	.............*...............................
	**..........**...............................
	.*...........................................
	.*.*.........................................
	..**.........................................
	.........................**...............*..
	.........................**...............*..
	..........................................***
	............................................*
	.............................................
	.............................................
	..*..........................................
	..*.*........................................
	..***........................................
	....*...........**...........................
	................*............................
	.................***.........................
	...................*.........................

:F166:  A {composite conduit}, one of the original sixteen
   {Herschel conduit}s, discovered by Paul Callahan in May 1997.  It is
   composed of two {elementary conduit}s, HFx107B + {BFx59H}.  The F166
   and {Lx200} conduits are the two original {dependent conduit}s
   (several more have since been discovered).  After 166 ticks, it
   produces a {Herschel} at (49, 3) relative to the input.  Its
   {recovery time} is 116 ticks.  A {ghost Herschel} in the pattern
   below marks the output location:
	.................................**.....................
	..................................*.....................
	.................................*......................
	.................................**.....................
	........................................................
	........................................................
	.**.....................................................
	***.**..................................................
	.**.***.**..............................................
	***.**..**..........................**...............*..
	**..................................**...............*..
	.....................................................***
	.......................................................*
	........................................................
	........................................................
	........................................................
	......**................................................
	.....*.*......................................**........
	.....*.........................................*........
	....**.........................**...........***.........
	...............................**...........*...........
	........................................................
	........................................................
	.................**.....................................
	..................*.....................................
	...............***......................................
	...............*........................................
	...........................**...........................
	...........................*............................
	............................***.........................
	..............................*.........................
   The F166 can be made {Spartan} by replacing the {snake} with an
   {eater1} in one of two orientations.  The input shown here is a
   {Herschel great-grandparent}, since the input reaction is catalysed
   by the {transparent} block before the Herschel's standard form can
   appear.

:F171:  An {elementary conduit}, the seventeenth {Herschel conduit},
   discovered by Brice Due in August 2006 in a search using only
   {eater}s as {catalyst}s.  This was the first new Herschel conduit
   discovery since 1998.  After 171 ticks, it produces a {Herschel} at
   (29, -17) relative to the input.  A {ghost Herschel} in the pattern
   below marks the output location:
	..........*......................
	..........***....................
	.............*...................
	............**...................
	.....*...........................
	.....***.........................
	........*........................
	.......**........................
	.................................
	..............................*..
	....**........................*..
	.....*........................***
	.....*.*........................*
	......**.........................
	.................................
	.................................
	*................................
	***..............................
	...*.............................
	..**.............................
	.................................
	.................................
	.................................
	.................................
	.................................
	.................................
	.*...............................
	.*.*.............................
	.***.............................
	...*.............................
	.................................
	..........**.....................
	...........*.....................
	........***......................
	........*........................
     The conduit's {recovery time} is 227 ticks, slower than many of the
   original sixteen conduits because of the delayed destruction of a
   temporary blinker, though the circuit itself is clearly {Spartan}.
   The recovery time can be improved to 120 ticks by adding {sparker}s
   of various periods to suppress the blinker.  See {clock} for a
   period-2 example.
     The central eater in the group of three to the northwest can be
   removed to release an additional {glider} output signal on a
   {transparent} {lane}.

:factory:  Another word for {gun}, but not used in the case of glider
   guns.  The term is also used for a pattern that repeatedly
   manufactures objects other than {spaceship}s or {rake}s.  In this
   case the new objects do not move out of the way, and therefore must
   be used up in some way before the next one is made.  The following
   shows an example of a p144 gun which consists of a p144 block factory
   whose output is converted into gliders by a p72 oscillator.
	.......................**........................**
	.......................**........................**
	.........................................**........
	........................................*..*.......
	.........................................**........
	...................................................
	....................................***............
	....................................*.*............
	.........**.........................***............
	.........**.........................**.............
	........*..*.......................***.............
	........*..*.**....................*.*.............
	........*....**....................***.............
	..........**.**....................................
	...............................**..................
	.....................**.......*..*.................
	.....................**........**..................
	.................................................**
	.................................................**
	...................................................
	....**..................*..........................
	**....****..........**..**.***.....................
	**..**.***..........**....****.....................
	....*...................**.........................
   This gun is David Bell's improvement of the one Bill Gosper found in
   July 1994.  The p72 oscillator is by Robert Wainwright in 1990, and
   the block factory is {Achim's p144} minus one of its stabilizing
   blocks.  For a block factory using stable components and triggered by
   an input {Herschel}, see also {keeper}.

:familiar fours:  Common patterns of four identical objects.  The five
   commonest are {traffic light} (4 blinkers), {honey farm} (4
   beehives), {blockade} (4 blocks), {fleet} (4 ships, although really 2
   ship-ties) and {bakery} (4 loaves, although really 2 bi-loaves).
   Also sometimes included is {four skewed blocks}.

:fanout:  A mechanism that emits two or more objects of some type for
   each one that it receives.  Typically the objects are {glider}s or
   {Herschel}s; {glider duplicator}s are a special case.

:Fast Forward Force Field:  The following reaction found by Dieter
   Leithner in May 1994.  In the absence of the incoming LWSS the
   gliders would simply annihilate one another, but as shown they allow
   the LWSS to advance 11 spaces in the course of the next 6
   generations.
	.......*......*..
	........*......**
	..**..***.....**.
	**.**............
	****.........*...
	.**.........**...
	............*.*..
     The illusion of super-light-speed travel is caused by an LWSS that
   is always created, but is then destroyed in some cases, by a signal
   catching up to it from behind that necessarily never travels faster
   than the {speed of light}.  It is not possible to make any use of the
   apparent super-light-speed signal.  The front end of an output LWSS
   can't be distinguished from the alternative dying {spark} output
   until several more ticks have passed.  Not surprisingly, this extra
   time is enough to drop the average speed of information transmission
   safely below c.
     Leithner named the Fast Forward Force Field in honour of his
   favourite science fiction writer, the physicist Robert L. Forward.
   See also {star gate} and {speed booster}.

:fate:  The result of evolving a pattern until its final behaviour is
   known.  This answers such questions such as whether or not the
   pattern remains finite, what its growth rate is, what {period} the
   final state may settle into, and what its final {census} is.  All
   small Life objects seem to eventually settle down into a mix of
   oscillators, simple spaceships, and occasionally small puffers.  See
   {methuselah}, {soup}, {ash}.
     Most sufficiently large random patterns are expected to grow
   forever due to the production of {switch engine}s at their boundary.
   Engineered Life objects - and therefore also sufficiently large and
   unlikely random patterns - can have more interesting behaviour, such
   as {breeder}s, {sawtooth}s, and prime calculators.  Some objects have
   even been constructed or designed having an {unknown fate}.

:father:  = {parent}

:fd:  Abbreviation for {full diagonal}s.

:featherweight spaceship:  = {glider}

:fencepost:  Any pattern that stabilizes one end of a {wick}.

:Fermat prime calculator:  A pattern constructed by Jason Summers in
   January 2000 that exhibits {infinite growth} if and only if there are
   no Fermat primes greater than 65537.  The question of whether or not
   it really does exhibit infinite growth is therefore equivalent to a
   well-known and long-standing unsolved mathematical problem. It will,
   however, still be growing at generation 10^2585827975. The pattern is
   based on Dean Hickerson's {primer} and {caber tosser} patterns and a
   p8 {beehive} {puffer} by Hartmut Holzwart.

:F-heptomino:  Name given by Conway to the following {heptomino}.
	**..
	.*..
	.*..
	.***

:figure-8: (p8)  A {domino} {sparker} found by Simon Norton in 1970.
	***...
	***...
	***...
	...***
	...***
	...***

:filter:  Any {oscillator} used to delete some but not all of the
   {spaceship}s in a stream.  An example is the {blocker}, which can be
   positioned so as to delete every other {glider} in a stream of period
   8n+4, and can also do the same for {LWSS} streams.  Other examples
   are the {MW emulator} and {T-nosed p4} (either of which can be used
   to delete every other LWSS in a stream of period 4n+2), the
   {fountain} (which does the same for {MWSS} streams) and a number of
   others, such as the p6 {pipsquirter}, the {pentadecathlon} and the
   p72 oscillator shown under {factory}.  Another example, a p4
   oscillator deleting every other HWSS in a stream of period 4n+2, is
   shown below.  (The p4 oscillator here was found, with a slightly
   larger {stator}, by Dean Hickerson in November 1994.)
	..........****............
	....**...******...........
	****.**..****.**..........
	******.......**...........
	.****.....................
	..........................
	................**........
	..............*....*......
	..........................
	.............*.*..*.*.....
	...........****.**.****...
	........*.*....*..*....*.*
	........**.**.*....*.**.**
	...........*.*......*.*...
	........**.*.*......*.*.**
	........**.*..........*.**
	...........*.*.****.*.*...
	...........*.*......*.*...
	..........**.*.****.*.**..
	..........*..***..***..*..
	............*..****..*....
	...........**.*....*.**...
	...........*..*....*..*...
	............*..*..*..*....
	.............**....**.....

:filter stream:  A {stream} of {spaceship}s in which there are periodic
   gaps in the stream.  This can thin out another crossing stream by
   deleting the {spaceship}s in the second stream except where the gaps
   occur.  The filter stream is not affected by the deletions so that
   the same stream can thin out multiple other streams. The
   {Caterpillar} uses filter streams of {MWSS}s in which there is a gap
   every 6 spaceships.  Here is part of a filter stream that thins a
   glider stream by 2/3:
	................................*.............................
	.................................*............................
	...............................***............................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	.......................................*......................
	........................................*.....................
	......................................***.....................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................*...............
	...............................................*..............
	.............................................***..............
	..............................................................
	..............................................................
	..*.............*...........................*.............*...
	*...*.........*...*.......................*...*.........*...*.
	.....*.............*...........................*.............*
	*....*........*....*......................*....*........*....*
	.*****.........*****.......................*****.........*****

:finger:  A protruding cell in an {oscillator} or {dying spark}, with
   the ability to modify a nearby active reaction.  Like a {thumb}, a
   finger cell appears at the edge of a reaction envelope and is the
   only live cell in its row or column.  The finger spark remains alive
   for two ticks before dying, whereas a thumb cell dies after one tick.
   Because the key cell is kept alive for an extra tick, an alternate
   technical term is "held (orthogonal) bit spark".  A "held diagonal
   bit spark" is not possible in B3/S23 for obvious reasons.

:fire:  An encoded signal used in combination with {push} and {pull}
   {elbow operation}s in a simple {construction arm}.  When a FIRE
   signal is sent, the construction-arm elbow produces an output glider,
   usually at 90 degrees from the construction arm.  This terminology is
   generally used when there is only a single recipe for such a glider
   output, or only one recipe for each glider colour (e.g., FIRE WHITE,
   FIRE BLACK).

:fireship: (c/10 orthogonally, p10)  A variant of the {copperhead} with
   a trailing component that emits several large {spark}s, discovered by
   Simon Ekstrom on 20 March 2016.  The interaction between the
   copperhead and the additional component is minimal enough that the
   extension technically fits the definition of a {tagalong}.  However,
   the extension slightly modifies two of the {phase}s of the spaceship,
   starting two ticks after the phase shown below, so it's also valid to
   classify the fireship as a distinct spaceship.
	....**....
	...****...
	..........
	..******..
	...****...
	..........
	..**..**..
	**.*..*.**
	...*..*...
	..........
	..........
	....**....
	....**....
	..........
	.*.*..*.*.
	*..*..*..*
	*........*
	*........*
	**......**
	..******..

:fire-spitting: (p3)  Found by Nicolay Beluchenko, September 2003.
	...*......
	.***......
	*.........
	.*.***....
	.*.....*..
	..*..*....
	..*.*..*.*
	........**

:first natural glider:  The glider produced at T=21 during the
   {evolution} of a {Herschel}.  This is the most common signal output
   from a {Herschel conduit}.

:fish:  A generic term for {LWSS}, {MWSS} and {HWSS}, or, more
   generally, for any {spaceship}.  In recent years {*WSS} is much more
   commonly used to refer to the small orthogonal c/2 spaceships.

:fishhook:  = {eater1}

:fleet: (p1)  A common formation of two {ship-tie}s.
	....**....
	....*.*...
	.....**...
	.......**.
	**.....*.*
	*.*.....**
	.**.......
	...**.....
	...*.*....
	....**....

:flip-flop:  Any p2 {oscillator}.  However, the term is also used in two
   more specific (and non-equivalent) senses: (a) any p2 oscillator
   whose two {phase}s are mirror images of one another, and (b) any p2
   oscillator in which all {rotor} cells die from {underpopulation}.  In
   the latter sense it contrasts with {on-off}. The term has also been
   used even more specifically for the 12-cell flip-flop shown under
   {phoenix}.

:flip-flops:  Another name for the flip-flop shown under {phoenix}.

:flipper:  Any {oscillator} or {spaceship} that forms its mirror image
   halfway through its period.

:flotilla:  A {spaceship} composed of a number of smaller interacting
   spaceships.  Often one or more of these is not a true spaceship and
   could not survive without the support of the others.  The following
   example shows an {OWSS} escorted by two {HWSS}.
	....****.......
	...******......
	..**.****......
	...**..........
	...............
	...........**..
	.*............*
	*..............
	*.............*
	**************.
	...............
	...............
	....****.......
	...******......
	..**.****......
	...**..........

:fly:  A certain c/3 {tagalong} found by David Bell, April 1992. Shown
   here attached to the back of a small spaceship (also by Bell).
	..*...............................
	.*.*..............................
	.*.*......................*.*...*.
	.*.......................**.*.*..*
	...........***........*.........*.
	**.........**..*.**...*..****.....
	.*.*.........****..*.*..**....**..
	.**........*..*...***.....***.....
	..*.......*....*..**..**..*..*....
	...*..*...*....*..***.*.*....**...
	.......*.**....*..****.....*......
	....**...**....*..****.....*......
	....*.*...*....*..***.*.*....**...
	...**.....*....*..**..**..*..*....
	....*.*....*..*...***.....***.....
	.....*.......****..*.*..**....**..
	...........**..*.**...*..****.....
	...........***........*.........*.
	.........................**.*.*..*
	..........................*.*...*.

:fly-by deletion:  A reaction performed by a passing {convoy} of
   {spaceship}s which deletes a common stationary object without harming
   the convoy.  Fly-by deletion is often used in the construction of
   {puffer}s and {spaceship}s to clean up unwanted debris.
     For c/2 convoys this is not usually difficult since the {LWSS},
   {MWSS}, and {HWSS} {spaceship}s have such useful {spark}s.  However,
   some objects are more difficult to delete. For example, deleting a
   {tub} appears to require an unusual p4 spaceship.
	.......................*.........
	......................*.*........
	.......................*.........
	.................................
	.................................
	.................................
	................***..............
	***.............*..*.............
	*..*....***.....*...........***..
	*.......*..*....*...*.......*..*.
	*...*..*...*....*...*.......*....
	*......*.*...*..*...........*...*
	.*..**........*.*...........*...*
	.*****........*.............*....
	....**......*...***..........*.*.
	.**..............................
     The deletion of a {pond} appears to require a convoy which is 89
   cells in width containing a very unusual p4 spaceship which has 273
   cells.  There are small objects which have no known fly-by deletion
   reactions.  However, as in the case of {reanimation}, hitting them
   with the output of {rake}s is an effective brute force method.

:flying machine:  = {Schick engine}

:FNG:  = {first natural glider}.

:fore and back: (p2)  Compare {snake pit}.  Found by Achim Flammenkamp,
   July 1994.
	**.**..
	**.*.*.
	......*
	***.***
	*......
	.*.*.**
	..**.**

:forward glider:  A {glider} which moves at least partly in the same
   direction as the {puffer}(s) or {spaceship}(s) under consideration.

:fountain: (p4)  Found by Dean Hickerson in November 1994, and named by
   Bill Gosper.  See also {filter} and {superfountain}.
	.........*.........
	...................
	...**.*.....*.**...
	...*.....*.....*...
	....**.**.**.**....
	...................
	......**...**......
	**...............**
	*..*...*.*.*...*..*
	.***.*********.***.
	....*....*....*....
	...**.........**...
	...*...........*...
	.....*.......*.....
	....**.......**....

:four skewed blocks: (p1)  The following {constellation}, sometimes
   considered to be one of the {familiar fours}.
	...**.....
	...**.....
	..........
	..........
	..........
	........**
	**......**
	**........
	..........
	..........
	..........
	.....**...
	.....**...
   This is most commonly created by a symmetric {2-glider collision}:
	.**.....
	*.*.....
	..*..*..
	.....*.*
	.....**.

:fourteener: (p1)
	....**.
	**..*.*
	*.....*
	.*****.
	...*...

:fox: (p2)  This is the smallest asymmetric p2 oscillator.  Found by
   Dave Buckingham, July 1977.
	....*..
	....*..
	..*..*.
	**.....
	....*.*
	..*.*.*
	......*

:freeze-dried:  A term used for a {glider constructible} {seed} that can
   activated in some way to produce a complex object.  For example, a
   "freeze-dried salvo" is a constellation of constructible objects
   which, when {trigger}ed by a single glider, produces a unidirectional
   glider {salvo}, and nothing else.  Freeze-dried salvos can be useful
   in {slow salvo} constructions, especially when an active circuit has
   to destroy or reconstruct itself in a limited amount of time.
   Gradual modification by a {construction arm} may be too slow, or the
   circuit doing the construction may itself be the object that must be
   modified.
     The concept may be applied to other types of objects.  For example,
   one possible way to build a gun for a {waterbear} would be to program
   a construction arm to build a freeze-dried waterbear seed, and then
   trigger it when the construction is complete.

:French kiss: (p3)  Found by Robert Wainwright, July 1971.
	*.........
	***.......
	...*......
	..*..**...
	..*....*..
	...**..*..
	......*...
	.......***
	.........*
   For many years this was one of the best-known small oscillators with
   no known {glider synthesis}.  In October 2013 Martin Grant completed
   a 23-glider construction.

:frog II: (p3)  Found by Dave Buckingham, October 1972.
	..**...**..
	..*.*.*.*..
	....*.*....
	...*.*.*...
	...**.**...
	.**.....**.
	*..*.*.*..*
	.*.*...*.*.
	**.*...*.**
	....***....
	...........
	...*.**....
	...**.*....

:frothing puffer:  A frothing puffer (or a frothing spaceship) is a
   {puffer} (or {spaceship}) whose back end appears to be unstable and
   breaking apart, but which nonetheless survives.  The {exhaust}
   festers and clings to the back of the puffer/spaceship before
   breaking off. The first known frothing puffers were c/2, and most
   were found by slightly modifying the back ends of p2 spaceships.  A
   number of these have periods which are not a multiple of 4 (as with
   some {line puffer}s).  Paul Tooke has also found c/3 frothing
   puffers.
     The following p78 c/2 frothing puffer was found by Paul Tooke in
   April 2001.
	.......*.................*.......
	......***...............***......
	.....**....***.....***....**.....
	...**.*..***..*...*..***..*.**...
	....*.*..*.*...*.*...*.*..*.*....
	.**.*.*.*.*....*.*....*.*.*.*.**.
	.**...*.*....*.....*....*.*...**.
	.***.*...*....*.*.*....*...*.***.
	**.........**.*.*.*.**.........**
	............*.......*............
	.........**.*.......*.**.........
	..........*...........*..........
	.......**.*...........*.**.......
	.......**...............**.......
	.......*.*.*.***.***.*.*.*.......
	......**...*...*.*...*...**......
	......*..*...*.*.*.*...*..*......
	.........**....*.*....**.........
	.....**....*...*.*...*....**.....
	.........*.**.*...*.**.*.........
	..........*.*.*.*.*.*.*..........
	............*..*.*..*............
	...........*.*.....*.*...........

:frothing spaceship:  See {frothing puffer}.

:frozen:  = {freeze-dried}.

:full diagonal:  Diagonal distance measurement, abbreviated "fd", often
   appropriate when a {construction arm} {elbow} or similar
   diagonally-adjustable mechanism is present.

:fumarole: (p5)  Found by Dean Hickerson in September 1989.  In terms of
   its 7x8 bounding box this is the smallest p5 oscillator.
	...**...
	.*....*.
	.*....*.
	.*....*.
	..*..*..
	*.*..*.*
	**....**

:fuse:  A {wick} {burn}ing at one end.  For examples, see {baker},
   {beacon maker}, {blinker ship}, {boat maker}, {cow}, {harvester},
   {lightspeed wire}, {pi ship}, {reverse fuse}, {superstring} and
   {washerwoman}.  Useful fuses are usually {clean}, but see also
   {reburnable fuse}.
     A fuse can {burn} arbitrarily slowly, as demonstrated by the
   example {Blockic} fuse below.  A {signal}, alternating between
   {glider} and {MWSS} form, travels up and down between two rows of
   blocks in a series of {one-time} {turner} reactions.  The spacing
   shown here causes the fuse to burn 24 cells to the right every 240
   generations, for a speed of c/10.  Moving the bottom half further
   from the top half by any even number of cells will slow down the
   burning even further.
	.........**......................**......................
	.........**......................**......................
	.........................................................
	.........................................................
	.....**.......**.............**.......**.............**..
	.**..**.......**.........**..**.......**.........**..**..
	.**................**....**................**....**......
	...................**......................**............
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	............**....**................**....**.............
	............**....**................**....**.............
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	**....**................**....**................**....**.
	**....**................**....**................**....**.
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.**....**......................**......................**
	*.*....**....**................**....**................**
	..*..........**..**.......**.........**..**.......**.....
	.................**.......**.............**.......**.....
	.........................................................
	.........................................................
	.....................**......................**..........
	.....................**......................**..........

:Fx119:  An {elementary conduit}, one of the original sixteen
   {Herschel conduit}s, discovered by Dave Buckingham in September 1996.
   After 119 ticks, it produces an inverted {Herschel} at (20, 14)
   relative to the input.  Its recovery time is 231 ticks; this can be
   reduced somewhat by suppressing the output Herschel's glider, or by
   adding extra {catalyst}s to make the reaction settle more quickly. A
   {ghost Herschel} in the pattern below marks the output location:
	*......................
	*.*....................
	***....................
	..*....................
	.......................
	.......................
	.......................
	.......................
	.......................
	.......................
	.......................
	.......................
	.......................
	.......................
	.......................
	.........**...........*
	....**...**.........***
	....**..............*..
	....................*..
	.......................
	...**..................
	....*....**............
	.***.....**............
	.*.....................

:Fx119 inserter:  A {Herschel-to-glider} {converter} and {edge shooter}
   based on an {Fx119} Herschel conduit:
	.........*....................
	.........*.*..................
	.........***..................
	...........*..................
	..............................
	..............................
	..............................
	..............................
	..**......**..................
	...*.......*..................
	***.....***...................
	*.......*.....................
	..............................
	..............................
	..............................
	..................**..........
	.............**...**..........
	.............**...............
	..............................
	..............................
	............**............**..
	.............*....**......*...
	..........***.....**.......***
	..........*..................*
     This edge shooter has an unusually high 27{hd} clearance, one of
   the highest known for a single small component.  The only known
   higher-clearance edge shooters are injectors making use of multiple
   interacting spaceships.  This makes the Fx119 inserter ideal for the
   construction of wide {convoy}s whose total width can fit within its
   clearance distance.
     The component creates a large cloud of {smoke} behind its emitted
   glider which lasts for over 90 generations.  In spite of this, many
   tightly packed convoys can be made by injecting later gliders behind
   others in the convoy, helped along by the insertion reaction which is
   able to catch up to the existing gliders.  The Fx119 inserter can
   place a glider on the same lane as a passing glider and as close as
   15 ticks behind, which is only one step away from the minimum
   possible following distance.

:Fx153:  A {composite conduit}, one of the original sixteen
   {Herschel conduit}s, discovered by Paul Callahan in February 1997.
   It is made up of two {elementary conduit}s, HF94B + {BFx59H}. After
   153 ticks, it produces an inverted {Herschel} at (48, -4) relative to
   the input.  Its {recovery time} is 69 ticks.  It can be made
   {Spartan} by replacing the {snake} with an {eater1} in one of two
   orientations.  A {ghost Herschel} in the pattern below marks the
   output location:
	.........................**..........................
	**........................*..........................
	.*.............**......***...........................
	.*.*...........**......*.............................
	..**.................................................
	.....................................................
	.....................................................
	.....................................................
	....................................................*
	..................................................***
	.................................**...............*..
	..*..............................**...............*..
	..*.*................................................
	..***................................................
	....*................................................
	.....................................................
	.....................................................
	..............................**.....................
	..............................*......................
	...........**...**.............*.....................
	............*...*.............**.....................
	.........***.....***.................................
	.........*.........*.................................

:Fx158:  An {elementary conduit}, one of the original sixteen
   {Herschel conduit}s, discovered by Dave Buckingham in July 1996.
   After 158 ticks, it produces an inverted {Herschel} at (27, -5)
   relative to the input.  Its {recovery time} is 176 ticks.  It is the
   only known small conduit that does not produce its output Herschel
   via the usual {Herschel great-grandparent}, so it cannot be followed
   by a {dependent conduit}.  A {ghost Herschel} in the pattern below
   marks the output location:
	.........*....**..............
	........*.*..*.*.......**.....
	.......*..****.........*......
	.......*.*....*......*.*......
	.....***.**..**......**.......
	....*.........................
	.*..****.**...................
	.***...*.**...................
	....*.........................
	...**.........................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	.............................*
	...........................***
	...........................*..
	...........................*..
	*.............................
	*.*...........................
	***...........................
	..*...........................
	..............................
	...............**.............
	.........**....*.*............
	..........*......*............
	.......***.......**...........
	.......*......................

:Fx176:  A {composite conduit}, one of the original sixteen
   {Herschel conduit}s, discovered by Paul Callahan in October 1997.  It
   is made up of three {elementary conduit}s, HF95P + PF35W + WFx46H.
   After 176 ticks, it produces an inverted {Herschel} at (45, 0)
   relative to the input.  The {recovery time} of the standard form
   shown here is 92 ticks, but see the {PF35W} entry for a variant
   discovered in November 2017 that lowers the repeat time to 73 ticks.
   A {ghost Herschel} in the pattern below marks the output location.
	..............................**..................
	..............................**..................
	..................................................
	.................**...............................
	..................*...............................
	..................*.*.............................
	...................**.............................
	..................................................
	..................................................
	..............**..................................
	......*.......**..................................
	......***.........................................
	.........*........................................
	........**........................................
	..................................................
	**................................................
	.*................................................
	.*.*.....................................**.......
	..**......................................*.......
	..........................................*.*.....
	...........................................*.*....
	............................................*...**
	................................................**
	..................................................
	..................................................
	..*...............................................
	..*.*...............................**...........*
	..***...............................**.........***
	....*..........................................*..
	...............................................*..
	..............**........**........................
	..............**..**.....*........................
	..................*.*.***.........................
	....................*.*...........................
	....................**....**......................
	.........................*.*....**................
	.........................*......**................
	........................**........................

:Fx77:  An {elementary conduit}, one of the original sixteen
   {Herschel conduit}s, discovered by Dave Buckingham in August 1996.
   After 77 ticks, it produces an inverted {Herschel} at (25, -8)
   relative to the input.  Its {recovery time} is 61 ticks; this can be
   reduced slightly by suppressing the output Herschel's glider, as in
   the {L112} case.  A {pipsquirter} can replace the blinker-suppressing
   eater to produce an extra glider output.  It is one of the simplest
   known {Spartan} conduits, and one of the few {elementary conduit}s in
   the original set of sixteen.
     In January 2016, Tanner Jacobi discovered a {Spartan} method of
   extracting an extra glider output (top variant below).  A
   {ghost Herschel} marks the output location for each variant.
	.*............................
	.***..........................
	....*.........................
	...**...........**...........*
	................**.........***
	...........................*..
	...........................*..
	..............................
	..............................
	..............................
	..*...........................
	..*.*.........................
	..***.........................
	....*.........................
	..............................
	..............................
	..............................
	..............................
	..............................
	............**......**........
	...........*..*.....**........
	...........*..*...............
	............**................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	*.............................
	***...........................
	...*..........................
	..**...........**...........*.
	...............**.........***.
	..........................*...
	..........................*...
	..............................
	..............................
	..............................
	.*............................
	.*.*..........................
	.***..........................
	...*..........................
	..............................
	..............................
	..............................
	..............................
	..............................
	................**............
	................*.*...........
	..................*...........
	..................**..........

:G4 receiver: An alternate {Herschel receiver} discovered by Sergei
   Petrov on 28 December 2011, using his previous {glider to 2 blocks}
   {converter}.  In the pattern below the {Herschel} output is marked by
   a {ghost Herschel}.  A {glider} also escapes to the northwest.  For
   an explanation of the "G4" describing the {tandem glider} input, see
   {Gn}.
	................................*.*.......................
	................................**........................
	.................................*........................
	..........................................................
	..........................................................
	..........................................................
	..........................................................
	................**........................................
	................**....................*...................
	...........................*.*......***...................
	...........................**......*......................
	............................*......**.....................
	..........................................................
	..........................................................
	..........................................................
	**........................................................
	**........................................................
	......................................**...............*..
	...........**.........................**...............*..
	...........**..........................................***
	.......................**................................*
	........*..........**..**.................................
	......***..........**.....................................
	.....*....................................................
	.....**........................**.........................
	.................**............*..........................
	.................**......*......***.......................
	........................*.*.......*.......................
	.........................*................................

:Gabriel's p138: (p138)  The following {oscillator} found by Gabriel
   Nivasch in October 2002.
	.......***.....
	......*..*.....
	.......*...*...
	..*.....***....
	...*.....*.....
	**.**..........
	*..*.........*.
	*.*.........*.*
	.*.........*..*
	..........**.**
	.....*.....*...
	....***.....*..
	...*...*.......
	.....*..*......
	.....***.......

:galaxy:  = {Kok's galaxy}

:Game of Life:  = {Life}

:Game of Life News:  A blog reporting on new Life discoveries, started
   by Heinrich Koenig in December 2004, currently found at
   {http://pentadecathlon.com/lifenews/}.

:Garden of Eden:  A configuration of ON and OFF cells that can only
   occur in generation 0.  (This term was first used in connection with
   cellular automata by John W. Tukey, many years before Life.)  It was
   known from the start that there are Gardens of Eden in Life, because
   of a theorem by Edward Moore that guarantees their existence in a
   wide class of cellular automata.  Explicit examples have since been
   constructed, the first by Roger Banks, et al. at MIT in 1971. This
   example was 9 x 33.  In 1974 J. Hardouin-Duparc et al. at the
   University of Bordeaux 1 produced a 6 x 122 example.  The following
   shows a 12 x 12 example found by Nicolay Beluchenko in February 2006,
   based on a 13 x 12 one found by Achim Flammenkamp in June 2004.
	..*.***.....
	**.*.*****.*
	*.*.**.*.*..
	.****.*.***.
	*.*.**.***.*
	.***.**.*.*.
	..*...***..*
	.*.**.*.*.*.
	***.****.*.*
	**.****...*.
	.*.*.**..*..
	.**.*..**.*.
     Below is a 10x10 Garden of Eden found by Marijn Heule, Christiaan
   Hartman, Kees Kwekkeboom, and Alain Noels in 2013 using SAT-solver
   techniques.  An exhaustive search of 90-degree rotationally symmetric
   10x10 patterns was possible because the symmetry reduces the number
   of unknown cells by a factor of four.
	.*.***.*..
	..*.*.*..*
	*.***..**.
	.*.*****.*
	*..*..****
	****..*..*
	*.*****.*.
	.**..***.*
	*..*.*.*..
	..*.***.*.
     Steven Eker has since found several asymmetrical Gardens of Eden
   that are slightly smaller than this in terms of bounding box area.
   Patterns have also been found that have only Garden of Eden
   {parent}s.  For related results see {grandparent}.

:Gemini: ((5120,1024)c/33699586 obliquely, p33699586)  The first
   {self-constructing} spaceship, and also the first {oblique}
   spaceship.  It was made public by Andrew Wade on 18 May 2010.  It was
   the thirteenth explicitly constructed spaceship velocity in Life, and
   made possible an infinite family of related velocities.  The Gemini
   spaceship derives its name from the Latin "gemini", meaning twins,
   describing its two identical halves, each of which contains three
   Chapman-Greene {construction arm}s. A tape of gliders continually
   relays between the two halves, instructing each to delete its parent
   and construct a daughter configuration.

:Gemini puffer:  See {Pianola breeder}.

:Geminoid:  A type of self-constructing circuitry that borrows key ideas
   from Andrew Wade's {Gemini} spaceship, but with several
   simplifications.  The main feature common to the Gemini spaceship is
   the construction recipe encoding method.  Information is stored
   directly, and much more efficiently, in the timings of moving
   gliders, rather than in a static tape with 1s and 0s encoded by the
   presence of small stationary objects.
     Unlike the original Gemini, Geminoids have {ambidextrous}
   construction arms, initially using glider pairs on two lanes
   separated by 9{hd}, 10hd, or 0hd. The design was the basis for the
   {linear propagator} and the {Demonoid}s.  A more recent development
   is a Geminoid toolkit using a {single-channel} construction arm,
   which allows for the possibility of multiple elbows with no loss of
   efficiency, or the construction of temporary lossless elbows.
   Compare {slow elbow}.
     Other new developments that could be considered part of the
   extended "Geminoid" toolkit include {freeze-dried} construction
   salvos and seeds, used when objects must be built within a short time
   window, and self-destruct circuits, which are used as an alternative
   to a {destructor arm} to clean up temporary objects in a similarly
   short window.

:generation:  The fundamental unit of time.  The starting pattern is
   generation 0.

:germ: (p3)  Found by Dave Buckingham, September 1972.
	....**....
	.....*....
	...*......
	..*.****..
	..*....*..
	.**.*.....
	..*.*.****
	*.*.*....*
	**...***..
	.......**.

:gfind:  A program by David Eppstein which uses {de Bruijn graph}s to
   search for new {spaceship}s.  It was with gfind that Eppstein found
   the {weekender}, and Paul Tooke later used it to find the {dragon}.
   It is available at {http://www.ics.uci.edu/~eppstein/ca/gfind.c} (C
   source code only).
     Compare {lifesrc}.

:ghost Herschel:  A dying {spark} made by removing one cell from the
   {Herschel} heptomino.  This particular spark has the advantage that,
   when placed in a conduit to mark the location of an input or output
   Herschel, it disappears cleanly without damaging adjacent catalysts,
   even in {dependent conduit}s with a block only two cells away.
	*..
	*..
	***
	..*

:GIG:  A glider injection gate.  This is a device for {inject}ing a
   {glider} into a glider {stream}.  The injected glider is synthesized
   from one or more incoming {spaceship}s assisted by the presence of
   the GIG.  (This contrasts with some other glider injection reactions
   which do not require a GIG,  as in {inject}.)  Gliders already in the
   glider stream pass through the GIG without interfering with it.  A
   GIG usually consists of a small number of oscillators.
     For example, in July 1996 Dieter Leithner found the following
   reaction which allows the construction of a pseudo-period 14 glider
   stream.  It uses two {LWSS} streams, a {pentadecathlon} and a
   {volcano}.
	.*...........................
	..*..........**..............
	***.........***..............
	............**.*.............
	.....*.......***.............
	...*.*........*..............
	....**.......................
	.............................
	......................****...
	.....................******..
	....................********.
	............*......**......**
	...**.....*.*.......********.
	.**.**.....**........******..
	.****..........*......****...
	..**............*............
	..............***............
	.............................
	.............................
	.............................
	.....*******.................
	...***.***.***...............
	..*....***....*..............
	...****.*.***.*..............
	.............*...............
	..*.**.*.*.*.................
	..**.*.*.*.**................
	......*..*.*.................
	.......**..*.................
	...........**................
     Glider injection gates are useful for building glider {gun}s with
   {pseudo}-periods that are of the form nd, where n is a positive
   integer, and d is a proper divisor of some convenient base gun period
   (such as 30 or 46), with d > 13.

:glasses: (p2)  Compare {scrubber} and {spark coil}.
	....*........*....
	..***........***..
	.*..............*.
	.*..***....***..*.
	**.*...*..*...*.**
	...*...****...*...
	...*...*..*...*...
	....***....***....
	..................
	....**.*..*.**....
	....*.**..**.*....

:glider: (c/4 diagonally, p4)  The smallest, most common and first
   discovered {spaceship}.  This was found by Richard Guy in 1970 while
   Conway's group was attempting to track the {evolution} of the
   {R-pentomino}.  The name is due in part to the fact that it is
   {glide symmetric}.  (It is often stated that Conway discovered the
   glider, but he himself has said it was Guy.  See also the cryptic
   reference ("some guy") in {Winning Ways}.)
	***
	*..
	.*.
   The term "glider" is also occasionally (mis)used to mean "spaceship".

:glider-block cycle:  An infinite {oscillator} based on the following
   reaction (a variant of the {rephaser}).  The oscillator consists of
   copies of this reaction displaced 2n spaces from one another (for
   some n>6) with blocks added between the copies in order to cause the
   reaction to occur again halfway through the period.  The period of
   the resulting infinite oscillator is 8n-20.  (Alternatively, in a
   cylindrical universe of width 2n the oscillator just consists of two
   gliders and two blocks.)
	...**...
	...**...
	........
	........
	..*..*..
	*.*..*.*
	.**..**.

:glider constructible:  See {glider synthesis}.

:glider construction:  = {glider synthesis}.

:glider duplicator:  Any reaction in which one input {glider} is
   converted into two output gliders.  This can be done by {oscillator}s
   or {spaceship}s, or by {Herschel conduit}s or other {signal}
   {circuit}ry such as the {stable} example shown under {splitter}.  The
   most useful glider duplicators are those with low {period}s.
     The following period 30 glider duplicator demonstrates a simple
   mechanism found by Dieter Leithner.  The input glider stream comes in
   from the upper left, and the output glider streams leave at the upper
   and lower right.  One of the output glider streams is inverted, so an
   {inverting reflector} is required to complete the duplicator.  To
   produce non-parallel output, an {inline inverter} could be
   substituted for the northmost p30 glider gun.
	.......*....**.......................**.........
	........*....*.......................**.........
	......***....*.*.......*..........**......*...**
	..............**.......*.*.......***.....*...*.*
	..........................**......**......*****.
	..........................**.........**....***..
	..........................**.........**.........
	.......................*.*......................
	.......................*........................
	................................................
	................................................
	........................**......................
	........................**......................
	................................................
	................................................
	................................................
	.........................***....................
	...........................*....................
	..........................*.....................
	................................................
	................................................
	.........*.*....................................
	.......*...*.....***............................
	**.....*.......*.*..*..**.......................
	**....*....*.......**..*..*.....................
	.......*...................*....................
	.......*...*..***..........*....................
	.........*.*...............*....................
	.......................*..*.....**..............
	.......................**.......*.*.............
	..................................*.............
	..................................**............
     Spaceship {convoy}s that can duplicate gliders are very useful
   since they (along with {glider turner}s) provide a means to clean up
   many dirty puffers by duplicating and turning output gliders so as to
   impact into the {exhaust} to clean it up.
     Glider duplicators and turners are known for backward gliders using
   p2 c/2 spaceships, and for forward gliders using p3 c/3 spaceships.
   These are the most general duplicators for these speeds.

:glider gun:  A {gun} that fires {glider}s.  For examples, see
   {Gosper glider gun}, {Simkin glider gun}, {new gun},  {p45 gun}.
     True-period glider guns are known for some low periods, and for all
   periods over 53 using {Herschel conduit} {technology}.  See {true}
   for a list of known true-period guns.  The lowest true-period gun
   possible is the {p14 gun} since that is the lowest possible period
   for any glider {stream}, but no example has yet been found.
     Pseudo-period glider guns are known for every period above 13.
   These are made by using multiple true-period guns of some multiple of
   the period, and glider {inject}ion methods to fill in the gaps.

:glider injection gate:  = {GIG}

:glider lane:  See {lane}.

:gliderless:  A {gun} is said to be gliderless if it does not use
   {glider}s.  The purist definition would insist that a glider does not
   appear anywhere, even incidentally.  For a long time the only known
   way to construct {LWSS}, {MWSS} and {HWSS} guns involved gliders, and
   it was not until April 1996 that Dieter Leithner constructed the
   first gliderless gun (a p46 LWSS gun).
     In October 2017 Matthias Merzenich used two copies of
   {Tanner's p46} to create a p46 MWSS gun.  This is the smallest known
   gliderless gun, and also the smallest known MWSS gun.
	......*.................................
	......***...............................
	.........*..............................
	........**..............................
	.....*..................................
	...***..................................
	..*.....................................
	..**....................................
	........................................
	..**.......*.*..*.*.....................
	..*.*......*..*...*.....................
	...*.....**...*.*.*.....................
	***.......***.*.........................
	*......**.....**........***.............
	.......**....**........*...*............
	.......**...*.........*.....*...........
	.......**.*.*........*...*...*..........
	.......**.*.*........*.......*.....**...
	.....................*.*...*.*.....**...
	.................**...**...**...........
	..........**....*.*.....................
	......**..**....*...................**..
	.....*.*.......**...................*...
	.....*.............**................***
	....**..............*....*.............*
	....................*.*.*.*.............
	.....................**.**.*............
	...........................*............
	...........................**...........

:glider pair:  Two gliders travelling in the same direction with a
   specific spacetime offset.  In a {transceiver} the preferred term is
   {tandem glider}.  For several years, glider pairs on {lane}s
   separated by 9 or 10 {half diagonal}s were the standard building
   blocks in {Geminoid} {construction arm} {recipe}s.  In more recent
   0hd and {single-channel} construction toolkits, all gliders share the
   same lane, but glider pairs and {singleton}s are still important
   concepts.

:glider-producing switch engine:  See {stabilized switch engine}.

:glider pusher:  An arrangement of a {queen bee shuttle} and a
   {pentadecathlon} that can push the path of a passing glider out by
   one half-diagonal space.  This was found by Dieter Leithner in
   December 1993 and is shown below.  It is useful for constructing
   complex {gun}s where it may be necessary to produce a number of
   gliders travelling on close parallel paths.  See also {edge shooter}.
	.........**..............
	.........**..............
	.........................
	..........*..............
	.........*.*.............
	.........*.*.............
	..........*..............
	.........................
	.........................
	.......**.*.**...........
	.......*.....*...........
	........*...*............
	.*.......***.............
	..*......................
	***......................
	.........................
	.........................
	.................*....*..
	...............**.****.**
	.................*....*..

:glider recipe:  = {glider synthesis}.

:glider reflector:  See {reflector}.

:gliders by the dozen: (stabilizes at time 184)  In early references
   this is usually shown in a larger form whose generation 1 is
   generation 8 of the form shown here.
	**..*
	*...*
	*..**

:glider stopper:  A {Spartan} logic circuit discovered by Paul Callahan
   in 1996.  It allows a {glider} signal to pass through the circuit,
   leaving behind a beehive that can cleanly absorb a single glider from
   a perpendicular glider {stream}.  Two optional glider outputs are
   also shown.  The circuit can't be re-used until the beehive "bit" is
   cleared by the passage of at least one perpendicular input.  A
   similar mechanism discovered more recently is shown in the
   {beehive stopper} entry.
	.*...........................................
	..*..........................................
	***..........................................
	.............................................
	.............................................
	...................................*.........
	..................................*..........
	..................................***........
	.............................................
	...............................*.............
	...............................*.*...........
	...................**..........**............
	...................**........................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	...................**........................
	..................*..*.......................
	...................**........................
	..........................**.................
	..........................**.................
	...........................................**
	........**.................................*.
	.......*.*...............................*.*.
	.......*.................................**..
	......**.....................................
	.............................................
	.............................................
	.............................................
	.................**..........................
	................*.*..........................
	................*............................
	...............**............................

:glider synthesis:  Construction of an object by means of {glider}
   collisions.  It is generally assumed that the gliders should be
   arranged so that they could come from infinity.  That is, gliders
   should not have had to pass through one another to achieve the
   initial arrangement.
     Glider syntheses for all {still life}s and known {oscillator}s with
   at most 14 cells were found by Dave Buckingham.  As of June 2018,
   this limit has been increased to 18 cells.
     Perhaps the most interesting glider syntheses are those of
   {spaceship}s, because these can be used to create corresponding
   {gun}s and {rake}s.  Many of the c/2 spaceships that are based on
   {standard spaceship}s have been synthesized, mostly by Mark Niemiec.
   In June 1998 Stephen Silver found syntheses for some of the
   {Cordership}s (although it was not until July 1999 that Jason Summers
   used this to build a Cordership gun).  In May 2000, Noam Elkies
   suggested that a 2c/5 spaceship found by Tim Coe in May 1996 might be
   a candidate for glider synthesis.  Initial attempts to construct a
   synthesis for this spaceship got fairly close, but it was only in
   March 2003 that Summers and Elkies managed to find a way to perform
   the crucial last step.  Summers then used the new synthesis to build
   a c/2 forward rake for the 2c/5 spaceship; this was the first example
   in Life of a rake which fires spaceships that travel in the same
   direction as the rake but more slowly.
     A 3-glider synthesis of a {pentadecathlon} is shown in the diagram
   below.  This was found in April 1997 by Heinrich Koenig and came as a
   surprise, as it was widely assumed that anything using just three
   gliders would already be known.
	......*...
	......*.*.
	......**..
	..........
	***.......
	..*.......
	.*.....**.
	........**
	.......*..

:glider to 2 blocks: A {converter} discovered by Sergei Petrov on 8
   October 2011, used in his later {G4 receiver}.
	..........*.......**
	**......*.*.......**
	**.......**.........
	....................
	....................
	....................
	...........**.......
	...........**.......
	....................
	....................
	..............**....
	...............*....
	...............*.*..
	................**..
	....................
	....................
	....................
	........**..........
	........**..........

:glider to block:  A {converter} discovered by Sergei Petrov that places
   a block at its right edge in response to a single {glider} input.
   This has a variety of uses in {Herschel circuit}ry and other
   {signal}-processing applications.
	...........*....
	.....*.....***..
	.....***......*.
	........*....**.
	.......**.......
	................
	................
	................
	................
	................
	**..............
	**..........**..
	............*.*.
	.............*..
	................
	................
	................
	............**..
	..***.......*...
	....*........***
	...*...........*


:glider train:  A certain p64 c/2 orthogonal {puffer} that produces two
   rows of {block}s and two backward {glider} waves.  Ten of these were
   used to make the first {breeder}.
	..............................*............
	...............................*...........
	.........................*.....*...........
	....*.....................******.....******
	.....*..............................*.....*
	*....*....................................*
	.*****..............................*....*.
	......................................**...
	...........................................
	.....................................*.....
	....................................*......
	...................................**...**.
	...................................*.*...**
	....................................*...**.
	........................................*..
	...........................................
	........................................*..
	....................................*...**.
	...................................*.*...**
	...................................**...**.
	....................................*......
	.....................................*.....
	...........................................
	......................................**...
	.*****..............................*....*.
	*....*....................................*
	.....*..............................*.....*
	....*.....................******.....******
	.........................*.....*...........
	...............................*...........
	..............................*............

:glider turner:  Any reaction in which a {glider} is turned onto a new
   path by a {spaceship}, {oscillator}, or {still life} {constellation}.
   In the last two cases, the glider turner is usually called a
   {reflector} if the reaction is repeatable, or a {one-time} {turner}
   if the reaction can only happen once.
     Glider turners are easily built using {standard spaceship}s. The
   following diagram shows a convoy which turns a {forward glider} 90
   degrees, with the new glider also moving forwards.
	.........**.........
	........**.****.....
	.*.......******.....
	*.........****......
	***.................
	....................
	....................
	....................
	....................
	...*................
	.*...*..............
	*...................
	*....*..............
	*****...............
	....................
	....................
	.............******.
	.............*.....*
	.............*......
	..............*....*
	................**..
   Small rearrangements of the back two spaceships can alternatively
   send the output glider into any of the other three directions.
     See also {glider duplicator} and {reflector}.

:glide symmetric:  Undergoing simultaneous reflection and translation. A
   glide symmetric {spaceship} is sometimes called a {flipper}.

:Gn:  An abbreviation specific to {converter}s that produce multiple
   {glider}s.  A "G" followed by any integer value means that the
   converter produces a {tandem glider} - two parallel glider outputs
   with lanes separated by the specified number of {half diagonal}s.

:gnome:  = {fox}

:GoE:  = {Garden of Eden}

:GoL:  = {Game of Life}

:Golly:  A cross-platform open source Life program by Andrew Trevorrow
   and Tomas Rokicki.  Unlike most Life programs it includes the ability
   to run patterns using the {hashlife} algorithm.  It is available from
   {http://golly.sourceforge.net}.

:Gosper glider gun:  The first known {gun}, and indeed the first known
   finite pattern displaying {infinite growth}, found by Bill Gosper in
   November 1970.  This period 30 gun remains the smallest known gun in
   terms of its bounding box, though some variants of the p120
   {Simkin glider gun} have a lower population. Gosper later constructed
   several other guns, such as {new gun} and the p144 gun shown under
   {factory}.  See also {p30 gun}.
	........................*...........
	......................*.*...........
	............**......**............**
	...........*...*....**............**
	**........*.....*...**..............
	**........*...*.**....*.*...........
	..........*.....*.......*...........
	...........*...*....................
	............**......................

:Gotts dots:  A 41-cell 187x39 {superlinear growth} pattern found by
   Bill Gosper in March 2006, who named it in honour of Nick Gotts,
   discoverer of many other low-population superlinear patterns, such as
   {Jaws}, the {mosquito}es, {teeth}, {catacryst} and {metacatacryst}.
   See {switch-engine ping-pong} for the lowest-population
   {superlinear growth} pattern as of July 2018, along with a list of
   the record-holders.
     Collisions within the pattern cause it to sprout its Nth
   {switch engine} at generation T = ~224n-6.  The population of the
   pattern at time t is asymptotically proportional to t times log(t),
   so the growth rate is O(t ln(t)), faster than {linear growth} but
   slower than {quadratic growth}.

:gourmet: (p32)  Found by Dave Buckingham in March 1978.  Compare with
   {pi portraitor} and {popover}.
	..........**........
	..........*.........
	....**.**.*....**...
	..*..*.*.*.....*....
	..**....*........*..
	................**..
	....................
	................**..
	*.........***..*.*..
	***.......*.*...*...
	...*......*.*....***
	..*.*..............*
	..**................
	....................
	..**................
	..*........*....**..
	....*.....*.*.*..*..
	...**....*.**.**....
	.........*..........
	........**..........

:gp:  = {glider pair}

:GPSE:  = {glider-producing switch engine}

:grammar:  A set of rules for connecting {component}s together to make
   an object such as a {spaceship}, {oscillator} or {still life}.  For
   example, in August 1989 Dean Hickerson found a grammar for
   constructing an infinite number of short wide c/3 period 3
   spaceships, using 33 different components and a table showing the
   ways that they can be joined together.

:grandfather:  = {grandparent}

:grandfatherless:  A traditional name for a pattern with one or more
   {parent}s but no grandparent.  This was a hypothetical designation
   until May 2016.  See {grandparent} for details.

:grandparent:  A pattern is said to be a grandparent of the pattern it
   gives rise to after two generations.  For over thirty years, a
   well-known open problem was the question of whether any pattern
   existed that had a parent but no grandparent.  In 1972, {LifeLine}
   Volume 6 mentioned John Conway's offer of a $50 prize for a solution
   to the problem, but it remained open until May 2016 when a user with
   the conwaylife.com forum handle 'mtve' posted an example.
     Other patterns have since been found that have a grandparent but no
   great-grandparent, or a great-grandparent but no
   great-great-grandparent.  Further examples in this series almost
   certainly exist, but as of July 2018 none have yet been found.

:Gray counter: (p4)  Found in 1971.  If you look at this in the right
   way you will see that it cycles through the Gray codes from 0 to 3.
   Compare with {R2D2}.
	......*......
	.....*.*.....
	....*.*.*....
	.*..*...*..*.
	*.*.*...*.*.*
	.*..*...*..*.
	....*.*.*....
	.....*.*.....
	......*......

:gray ship:  = {grey ship}

:great on-off: (p2)
	..**....
	.*..*...
	.*.*....
	**.*..*.
	....**.*
	.......*
	....***.
	....*...

:grey counter:  = {Gray counter}  (This form is erroneous, as Gray is
   surname, not a colour.)

:grey ship:  A {spaceship} that contains a region with an average
   density of 1/2, and which is {extensible} in such a way that the
   region of average density 1/2 can be made larger than any given
   square region.
     See also {with-the-grain grey ship}, {against-the-grain grey ship}
   and {hybrid grey ship}.

:grin:  The following common {parent} of the {block}.  This name relates
   to the infamous {Cheshire cat}.  See also {pre-block}.
	*..*
	.**.

:grow-by-one object:  A pattern whose population increases by one cell
   every generation.  The smallest known grow-by-one object is the
   following 44-cell pattern (David Bell's one-cell improvement of a
   pattern found by Nicolay Beluchenko, September 2005).
	........**.......
	.......**........
	.........*.......
	...........**....
	..........*......
	.................
	.........*..**...
	.**.....**....*..
	**.....*.....*...
	..*....*.*...**..
	....*..*....**.*.
	....**.......**..
	........*....*.**
	.......*.*..*.**.
	........*........

:growing/shrinking line ship:  A {line ship} in which the line
   repeatedly grows and shrinks, resulting in a high-period {spaceship}.

:growing spaceship:  An object that moves like a {spaceship}, except
   that its front part moves faster than its back part and a {wick}
   extends between the two.  Put another way, a growing spaceship is a
   {puffer} whose output is burning {clean}ly at a slower rate than the
   puffer is producing it.  Examples include {blinker ship}s,
   {pi ship}s, and some {wavestretcher}s.

:G-to-H:  A {converter} that takes a {glider} as an input {signal} and
   produces a {Herschel} output, which can then be used by other
   {conduit}s.  G-to-Hs are frequently used in {stable} logic circuitry.
   Early examples include {Callahan G-to-H}, {Silver G-to-H}, and
   {p8 G-to-H} for periodic circuits.  A more compact recent example is
   the {syringe}.

:gull:  = {elevener}

:gun:  Any stationary pattern that emits {spaceship}s (or {rake}s)
   forever.  For examples see {double-barrelled}, {edge shooter},
   {factory}, {gliderless}, {Gosper glider gun}, {Simkin glider gun},
   {new gun} and {true}.

:gunstar:  Any of a series of glider {gun}s of period 144+72n (for all
   non-negative integers n) constructed by Dave Buckingham in 1990 based
   on his {transparent block reaction} and Robert Wainwright's p72
   oscillator (shown under {factory}).

:gutter:  A single straight line of cells along the axis of symmetry of
   a mirror-{symmetric} pattern.  Most commonly this is an orthogonal
   line, and the pattern is then odd-symmetric (as opposed to
   even-symmetric, where the axis of symmetry follows the boundary
   between two rows or columns of cells).
     The birth rule for Conway's Life trivially implies that if there
   are no live cells in the gutter of a symmetric pattern, new cells can
   never be born there.  For examples, see {44P5H2V0}, {60P5H2V0},
   {Achim's p4}, {brain}, {c/6 spaceship}, {centinal}, {p54 shuttle},
   {pufferfish}, {snail}, {spider}, and {pulsar} (in two orientations).

:half-baked knightship: ((6,3)c/2621440, p2621440)  A {self-supporting}
   {macro-spaceship} with adjustable period but fixed direction, based
   on the {half-bakery reaction}.  This was the first spaceship based on
   this reaction, constructed in December 2014 by Adam P. Goucher. It
   moves 6 cells horizontally and 3 cells vertically every 2621440+8N
   ticks, depending on the relative spacing of the two halves.  It is
   one of the slowest known {knightship}s, and the first one that was
   not a {Geminoid}. Chris Cain optimized the design a few days later to
   create the {Parallel HBK}.
     The spaceship produces gliders from near-diagonal lines of
   half-bakeries, which collide with each other at 180 degrees.  These
   collisions produce {monochromatic salvo}s that gradually build and
   trigger {seed}s, which in turn eventually construct small
   {synchronized} {salvo}s of gliders.  These re-activate the lines of
   half-bakeries, thus closing the cycle and moving the entire spaceship
   obliquely by (6,3).

:half bakery:  = {bi-loaf}.

:half-bakery reaction:  The key reaction used in the
   {half-baked knightship} and {Parallel HBK}, where a half-bakery is
   moved by (6,3) when a glider collides with it, and the glider
   continues on a new lane.  Ivan Fomichev noticed in May 2014 that
   pairs of these reactions at the correct relative spacing can create
   90-degree output gliders:
	.............................*.
	............................*..
	............................***
	...............................
	...............................
	...............................
	...............................
	...............................
	...............................
	...............................
	....................**.........
	...................*..*........
	...................*.*.........
	.................**.*..........
	........*.......*..*...........
	......**........*.*............
	.......**........*.............
	...............................
	....**.........................
	...*..*........................
	...*.*.........................
	.**.*..........................
	*..*...........................
	*.*............................
	.*.............................

:half diagonal:  A natural measurement of distance between parallel
   glider lanes, or between {elbow} locations in a {universal}
   {construction arm} {elbow operation} library.  If two gliders are in
   the same phase and exactly lined up vertically or horizontally, N
   cells away from each other, then the two glider {lane}s are
   considered to be N half diagonals (hd) apart.  Gliders that are an
   integer number of {full diagonal}s apart must be the same colour,
   whereas integer {half diagonal}s allow for both glider colours.  See
   {colour of a glider}, {linear propagator}.

:half fleet:  = {ship-tie}

:Halfmax:  A pattern that acts as a spacefiller in half of the Life
   plane, found by Jason Summers in May 2005. It expands in three
   directions at c/2, producing a triangular region that grows to fill
   half the plane.

:hammer:  To hammer a {LWSS}, {MWSS} or {HWSS} is to smash things into
   the rear end of it in order to transform it into a different type of
   {spaceship}.  A hammer is the object used to do the hammering. In the
   following example by Dieter Leithner an LWSS is hammered by two more
   LWSS to make it into an MWSS.
	*..*................
	....*...**..........
	*...*..***.....****.
	.****..**.*....*...*
	........***....*....
	.........*......*..*

:hammerhead:  A certain front end for {c/2 spaceship}s.  The central
   part of the hammerhead pattern is supported between two {MWSS}. The
   picture below shows a small example of a {spaceship} with a
   hammerhead front end (the front 9 columns).
	................*..
	.**...........*...*
	**.***.......*.....
	.*****.......*....*
	..*****.....*.****.
	......***.*.**.....
	......***....*.....
	......***.***......
	..........**.......
	..........**.......
	......***.***......
	......***....*.....
	......***.*.**.....
	..*****.....*.****.
	.*****.......*....*
	**.***.......*.....
	.**...........*...*
	................*..

:hand:  Any object used as a {slow salvo} {target} by a
   {construction arm}.

:handshake:  An old MIT name for {lumps of muck}, from the following
   form (2 generations on from the {stairstep hexomino}):
	..**.
	.*.**
	**.*.
	.**..

:harbor: (p5)  Found by Dave Buckingham in September 1978.  The name is
   by Dean Hickerson.
	.....**...**.....
	.....*.*.*.*.....
	......*...*......
	.................
	.....**...**.....
	**..*.*...*.*..**
	*.*.**.....**.*.*
	.*.............*.
	.................
	.*.............*.
	*.*.**.....**.*.*
	**..*.*...*.*..**
	.....**...**.....
	.................
	......*...*......
	.....*.*.*.*.....
	.....**...**.....

:harvester: (c p4 fuse)  Found by David Poyner, this was the first
   published example of a {fuse}.  The name refers to the fact that it
   produces debris in the form of {block}s which contain the same number
   of cells as the fuse has burnt up.
	................**
	...............*.*
	..............*...
	.............*....
	............*.....
	...........*......
	..........*.......
	.........*........
	........*.........
	.......*..........
	......*...........
	.....*............
	*****.............
	****..............
	*.**..............

:hashlife:  A Life algorithm by Bill Gosper that is designed to take
   advantage of the considerable amount of repetitive behaviour in many
   large patterns of interest.  It provides a means of evolving
   repetitive patterns millions (or even billions or trillions) of
   generations further than normal Life algorithms can manage in a
   reasonable amount of time.
     The hashlife algorithm is described by Gosper in his paper listed
   in the bibliography at the end of this lexicon.  Roughly speaking,
   the idea is to store subpatterns in a hash table so that the results
   of their {evolution} do not need to be recomputed if they arise again
   at some other place or time in the evolution of the full pattern.
   This does, however, mean that complex patterns can require
   substantial amounts of memory.
     Tomas Rokicki and Andrew Trevorrow implemented Hashlife into
   {Golly} in 2005.  See also {macrocell}.

:hassle:  See {hassler}.

:hassler:  An {oscillator} that works by hassling (repeatedly moving or
   changing) some object.  For some examples, see {Jolson},
   {baker's dozen}, {toad-flipper}, {toad-sucker} and {traffic circle}.
   Also see {p24 gun} for a good use of a {traffic light} {hassler}.

:hat: (p1)  Found in 1971.  See also {twinhat} and {sesquihat}.
	..*..
	.*.*.
	.*.*.
	**.**

:HBK:  = {half-baked knightship}

:hd:  Abbreviation for {half diagonal}.  This metric is used primarily
   for relative measurements of glider lanes, often in relation to
   {self-constructing} circuitry; compare {Gn}.

:heat:  For an {oscillator} or {spaceship}, the average number of cells
   which change state in each generation.  For example, the heat of a
   {glider} is 4, because 2 cells are born and 2 die every generation.
     For a period n oscillator with an r-cell {rotor} the heat is at
   least 2r/n and no more than r(1-(n mod 2)/n).  For n=2 and n=3 these
   bounds are equal.

:heavyweight emulator:  = {HW emulator}

:heavyweight spaceship:  = {HWSS}

:heavyweight volcano:  = {HW volcano}

:hebdarole: (p7)  Found by Noam Elkies, November 1997.  Compare
   {fumarole}.  The smaller version shown below was found soon after by
   Alan Hensel using a component found by Dave Buckingham in June 1977.
   The top ten rows can be stabilized by their mirror image (giving an
   {inductor}) and this was the original form found by Elkies.
	...........**...........
	....**...*....*...**....
	.*..*..*.*....*.*..*..*.
	*.*.*.**.*....*.**.*.*.*
	.*..*..*.*.**.*.*..*..*.
	....**....*..*....**....
	...........**...........
	.......*..*..*..*.......
	......*.**....**.*......
	.......*........*.......
	........................
	...**..............**...
	...*..****....****..*...
	....*.*.*.*..*.*.*.*....
	...**.*...****...*.**...
	.......**......**.......
	.........**..**.........
	.........*..*.*.........
	..........**............

:hectic: (p30)  Found by Robert Wainwright in September 1984.
	......................**...............
	......................**...............
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.........*..........**...**............
	.......*.*............***..............
	......*.*............*...*.............
	**...*..*.............*.*..............
	**....*.*..............*...............
	.......*.*......*.*....................
	.........*......**.....................
	.................*...*.................
	.....................**......*.........
	....................*.*......*.*.......
	...............*..............*.*....**
	..............*.*.............*..*...**
	.............*...*............*.*......
	..............***............*.*.......
	............**...**..........*.........
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	...............**......................
	...............**......................

:Heisenburp device:  A pattern which can detect the passage of a
   {glider} without affecting the glider's path or timing.  The first
   such device was constructed by David Bell in December 1992.  The
   term, coined by Bill Gosper, refers to the fact that Heisenberg's
   Uncertainty Principle fails to apply in the Life universe.  See also
   {stable pseudo-Heisenburp} and {natural Heisenburp}.
     The following is an example of the kind of reaction used at the
   heart of a Heisenburp device.  The glider at bottom right alters the
   reaction of the other two gliders without itself being affected in
   any way.
	*.....*....
	.**...*.*..
	**....**...
	...........
	...........
	...........
	.........**
	........*.*
	..........*

:Heisenburp effect:  See {Heisenburp device}.

:helix:  A convoy of {standard spaceship}s used in a {Caterpillar} to
   move some piece of debris at the speed of the Caterpillar.  The
   following diagram illustrates the idea.  The leading edge of this
   example helix, represented by the glider at the upper right in the
   pattern below, moves at a speed of 65c/213, or slightly faster than
   c/4.
	...............................*.............
	.................*............***............
	................***....***....*.**...........
	.........***....*.**...*..*....***..***......
	.........*..*....***...*.......**...*........
	.........*.......**....*...*.........*.......
	.........*...*.........*...*.................
	***......*...*.........*.....................
	*..*.....*..............*.*..................
	*.........*.*................................
	*............................................
	.*.*.........................................
	.............................................
	.............................................
	..........*..................................
	.........***.................................
	.........*.**................................
	..........***................................
	..........**.................................
	.............................................
	.............................................
	...............***...........................
	...............*..*....*.....***.............
	...............*......***....*..*....*.......
	...............*.....**.*....*......***......
	....***.........*.*..***.....*.....**.*......
	....*..*.............***......*.*..***.......
	....*................***...........***.......
	....*.................**...........***.......
	.....*.*............................**.......
	...........................................*.
	..........................................***
	.........................................**.*
	.........................................***.
	..........................................**.
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.........................................*...
	..............................***.......***..
	................***.....*....*..*......**.*..
	..........*....*..*....***......*......***...
	.........***......*....*.**.....*......***...
	.........*.**.....*.....***..*.*........**...
	..........***..*.*......***..................
	.*........***...........***..................
	***.......***...........**...................
	*.**......**.................................
	.***......................................*..
	.**......................................***.
	........................................**.*.
	........................................***..
	.........................................**..
	.........***.................................
	........*..*.................................
	...........*.................................
	...........*.................................
	........*.*..................................
     Adjustable-speed helices can produce a very wide range of spaceship
   speeds; see {Caterloopillar}.

:heptaplet:  Any 7-cell {polyplet}.

:heptapole: (p2)  The {barberpole} of length 7.
	**........
	*.*.......
	..........
	..*.*.....
	..........
	....*.*...
	..........
	......*.*.
	.........*
	........**

:heptomino:  Any 7-cell {polyomino}.  There are 108 such objects. Those
   with names in common use are the {B-heptomino}, the {Herschel} and
   the {pi-heptomino}.

:Herschel: (stabilizes at time 128)  The following pattern which occurs
   at generation 20 of the {B-heptomino}.
	*..
	*.*
	***
	..*
     The name is commonly ascribed to the Herschel heptomino's
   similarity to a planetary symbol.  William Herschel discovered Uranus
   in 1781. However, in point of fact a Herschel bears no particular
   resemblance to either of the symbols used for Uranus, but does
   closely resemble the symbol for Saturn. So the appropriate name might
   actually be "Huygens", but "Herschel" is now universally used by
   tradition.
     Herschels are one of the most versatile types of {signal} in stable
   circuitry.  {R-pentomino}es and {B-heptomino}es naturally evolve into
   Herschels, and {converter}s have also been found that change
   {pi-heptomino}es and several other signal types into Herschels, and
   vice versa.  See {elementary conduit}.

:Herschel circuit:  A series of {Herschel conduit}s or other components,
   connected by placing them so that the output {Herschel}s from early
   conduits become the input Herschels for later conduits.  Often the
   initial component is a {converter} accepting some other signal type
   as input - usually a glider, in which case a {syringe} is most
   commonly used.  The {Silver reflector} is a well-known early
   {Spartan} Herschel circuit from before the syringe was discovered,
   where the initial converter is a {Callahan G-to-H}.
     Sometimes a direct connection between two conduits is not possible
   due to unwanted gliders that destroy required {catalyst}s, or wanted
   gliders that are not able to escape.  In this case, small "spacer"
   conduits such as {F116}, {F117}, {Fx77}, {R64}, {L112}, or {L156} can
   be inserted between the other conduits to solve the problem.
     Some converter or {factory} conduits do not produce a Herschel as
   output, instead generating other useful results such as gliders,
   {boat}s or {MWSS}es.  See {Herschel-to-glider}, {demultiplexer}, and
   {H-to-MWSS} respectively for examples of these.  For those conduits
   which do produce an unwanted Herschel, an {eater} such as {SW-2} can
   be added to delete it.
     If the first and last conduits of a chain connect to each other in
   a loop then there is no need for a syringe to generate the first
   Herschel, or an eater to consume the last one.  The circuit becomes a
   self-supporting {Herschel loop}.  A loop is also formed by a
   {syringe} connected to a Herschel-to-glider converter, with the
   glider reflected back to the syringe's input with glider reflectors
   of the appropriate colour, usually {Snark}s.  In either case, if the
   loop has a surplus {glider} output, it becomes a {gun}; if no output
   is available it is an {emu}.

:Herschel climber:  Any {reburnable fuse} reaction involving
   {Herschel}s.  May refer specifically to the
   {(23,5)c/79 Herschel climber} used in the {waterbear}, or one of
   several similar reactions with various velocities.  See also
   {Herschel-pair climber}.

:Herschel component:  = {Herschel conduit}

:Herschel conduit:  A {conduit} that moves a {Herschel} from one place
   to another.  See also {Herschel loop}.
     Well over a hundred simple stable Herschel conduits are currently
   known.  As of June 2018 the number is approximately 150, depending on
   the precise definition of "simple" - e.g., fitting inside a 100x100
   bounding box, and producing output in no more than 300 {tick}s.  In
   general a Herschel conduit can be called "simple" if its active
   reaction does not return to a  Herschel stage except at its output.
   Compare {elementary conduit}, {composite conduit}.  A description of
   common usage in complex circuitry, using {syringe}s and {Snark}s to
   make compact connections, can be found in {Herschel circuit}.
     The original {universal} set consisted of sixteen stable Herschel
   conduits, discovered between 1995 and 1998 by Dave Buckingham (DJB)
   and Paul Callahan (PBC).  These are shown in the following table.  In
   this table, the number in "name/steps" is the number of {tick}s
   needed to produce an output Herschel from the input Herschel.  "m"
   tells how the Herschel is moved (R = turned right, L = turned left, B
   = turned back, F = unturned, f = flipped), and "dx" and "dy" give the
   displacement of the centre cell of the Herschel (assumed to start in
   the orientation shown above).
	-----------------------------------------
	name/steps  m     dx   dy     discovery
	-----------------------------------------
	{R64}       R     11    9   DJB, Sep 1995
	{Fx77}      Ff    25   -8   DJB, Aug 1996
	{L112}      L     12  -33   DJB, Jul 1996
	{F116}      F     32    1   PBC, Feb 1997
	{F117}      F     40   -6   DJB, Jul 1996
	{Bx125}     Bf    -9  -17   PBC, Nov 1998
	{Fx119}     Ff    20   14   DJB, Sep 1996
	{Fx153}     Ff    48   -4   PBC, Feb 1997
	{L156}      L     17  -41   DJB, Aug 1996
	{Fx158}     Ff    27   -5   DJB, Jul 1996
	{F166}      F     49    3   PBC, May 1997
	{Fx176}     Ff    45    0   PBC, Oct 1997
	{R190}      R     24   16   DJB, Jul 1996
	{Lx200}     Lf    17  -40   PBC, Jun 1997
	{Rx202}     Rf     7   32   DJB, May 1997
	{Bx222}     Bf    -6  -16   PBC, Oct 1998
	-----------------------------------------
     See also {Herschel transceiver}.

:Herschel descendant:  A common active pattern occurring at generation
   22 of a {Herschel}'s {evolution}:
	**..
	*.**
	...*
	.*.*
	.**.
   There are other evolutionary paths leading to the same pattern,
   including the modification of a {B-heptomino} implied by generation
   21 of a Herschel.

:Herschel great-grandparent:  A specific three-{tick} predecessor of a
   {Herschel}, commonly seen in {Herschel conduit} collections that
   contain {dependent conduit}s.  In some situations it is helpful to
   display the input reaction in this form instead of the standard
   Herschel form.
	.**....
	***.**.
	.**.***
	***.**.
	**.....
     Dependent conduit inputs are catalysed by a {transparent} block
   before the Herschel's standard form can appear, and before the
   Herschel's {first natural glider} is produced.  This means that these
   conduits will fail if an actual Herschel is placed in the "correct"
   input location for a dependent conduit.  Refer to {F166} or {Lx200}
   to see the correct relative placement of the standard transparent
   block catalyst.
     Almost all known Herschel conduits produce a Herschel
   great-grandparent near the end of their evolutionary sequence.  In
   the original {universal} set of Herschel conduits, {Fx158} is the
   only exception.

:Herschel loop:  A cyclic {Herschel track}.  Although no loop of length
   less than 120 generations has been constructed it is possible to make
   {oscillator}s of smaller periods by putting more than one Herschel in
   a higher-period track.  In this way oscillators, and in most cases
   {gun}s, of all periods from 54 onwards can now be constructed
   (although the p55 case is a bit strange, shooting itself with gliders
   in order to stabilize itself).  A mechanism for a period-52 loop was
   found in April 2018, but it includes a stage where the signal is
   carried by a triplet of {glider}s so it may not be considered to be a
   pure Herschel loop.  The missing period, 53, is a difficult case
   simply because 53 is prime and so no small sparkers or reflectors are
   available.
     See {Simkin glider gun} and {p256 gun} for the smallest known
   Herschel loops.  See also {emu} and {omniperiodic}.

:Herschel-pair climber:  Any {reburnable fuse} reaction involving pairs
   of {Herschel}s.  May refer specifically to the
   {31c/240 Herschel-pair climber} used in the {Centipede}, or one of
   several similar reactions with various velocities.  See also
   {Herschel climber}.

:Herschel receiver:  Any {circuit} that converts a {tandem glider} into
   a {Herschel} {signal}.  The following diagram shows a pattern found
   by Paul Callahan in 1996, as part of the first stable glider
   {reflector}.  Used as a receiver, it converts two parallel input
   gliders (with path separations of 2, 5, or 6) to an {R-pentomino}.
   The signal is then converted to a Herschel by one of several known
   mechanisms, the first of which was found by Dave Buckingham way back
   in 1972.  The second is {elementary conduit} {RF48H}, found by
   Stephen Silver in October 1997.  The receiver version shown below
   uses Buckingham's R-to-Herschel converter, which is made up of
   elementary conduit {RF28B} followed by {BFx59H}.
	...............................................*.*
	......................................**.......**.
	......................................**........*.
	...**.............................................
	...*..............................................
	....*.............................................
	...**.............................................
	............**....................................
	...........*.*....................................
	............*..............................*......
	......................................**...*.*....
	.....................................*..*..**.....
	**....................................**..........
	**.............................**.................
	...............................**.................
	..................................................
	..................................................
	..................................................
	..................................................
	..................................................
	..................................................
	............................................**....
	............................................**....
	........................................**........
	........................................*.*.......
	..........................................*.......
	..........................................**......
	.............................**...................
	.............................**...................
	..................................................
	..................................................
	...........................**.....................
	...........................**.....................

:Herschel stopper:  A method of cleanly suppressing a {Herschel} signal
   with an {asynchronous} {boat-bit}, discovered by Dean Hickerson.
   Here a {ghost Herschel} marks the location of the output signal, in
   cases where the boat-bit is not present.  Other boat-bit locations
   that allow for clean suppression of a Herschel are also known.
	....................................**
	.........................*..........*.
	.........................***.........*
	............................*.......**
	...........................**.........
	......................................
	........*.............................
	........***...........................
	...........*..........................
	..........**...........**...........*.
	.......................**.........***.
	..................................*...
	..................................*...
	......................................
	..........................*...........
	..........................**..........
	.........*...............*.*..........
	.........*.*..........................
	.........***..........................
	...........*.......................**.
	....................................*.
	.................................***..
	.................................*....
	......................................
	..**..................................
	...*..................................
	***....................**.............
	*......................*..............
	........................***...........
	..........................*...........
     This term is also sometimes used to refer to any mechanism that
   cleanly suppresses a Herschel.  These usually allow the Herschel's
   {first natural glider} to escape, so they are more commonly
   classified as {converter}s.  See {SW-2}.

:Herschel-to-glider:  The largest category of {elementary conduit}.
   Gliders are very common and self-supporting, so it's much easier to
   find these than any other type of output {signal}.  A large
   collection of these H-to-G {converter}s has been compiled, with many
   different output {lane}s and timings.  These can be used to
   synchronize multiple signals to produce {gun} patterns or complex
   logic circuitry.  See {NW31T120} for an example.

:Herschel track:  A {track} for {Herschel}s.  An equivalent term is
   {Herschel circuit}.  See also {B track}.

:Herschel transceiver:  An adjustable {Herschel conduit} made up of a
   {Herschel transmitter} and a {Herschel receiver}.  The intermediate
   stage consists of a {tandem glider} - two {glider}s on parallel
   {lane}s - so that the transmitter and receiver can be separated by
   any required distance. The conduit may be {stable}, or may contain
   low-period {oscillator}s.

:Herschel transmitter:  Any {Herschel}-to-two-{glider} {converter} that
   produces a {tandem glider} that can be used as input to a
   {Herschel receiver}.  If the gliders are far enough apart, and if one
   of the gliders is used only for cleanup, then the transmitter is
   {ambidextrous}:  with a small modification to the receiver, a
   suitably oriented mirror image of the receiver will also work.
     The following diagram shows a {stable} Herschel transmitter found
   by Paul Callahan in May 1997:
	......**...........
	.....*.*...........
	...***.............
	..*...*......*.....
	..**.**......***...
	.............*.*...
	...............*...
	...................
	...................
	**.*...............
	*.**...............
	...................
	...................
	...................
	...............**..
	...............*...
	................***
	..................*
   Examples of small reversible p6 and p7 transmitters are also known,
   and more recently several alternate {Herschel transceiver}s have been
   found with different lane spacing, e.g., 0, 2, 4, 6, and 13.

:Hertz oscillator: (p8)  Compare {negentropy}, and also {cauldron}.
   Found by Conway's group in 1970.
	...**.*....
	...*.**....
	...........
	....***....
	...*.*.*.**
	...*...*.**
	**.*...*...
	**.*...*...
	....***....
	...........
	....**.*...
	....*.**...

:hexadecimal:  = {beehive and dock}

:hexaplet:  Any 6-cell {polyplet}.

:hexapole: (p2)  The {barberpole} of length 6.
	**.......
	*.*......
	.........
	..*.*....
	.........
	....*.*..
	.........
	......*.*
	.......**

:hexomino:  Any 6-cell {polyomino}.  There are 35 such objects. For some
   examples see {century}, {stairstep hexomino}, {table}, {toad} and
   {Z-hexomino}.

:HF:  = {honey farm}

:HFx58B:  A common {Herschel} to {B-heptomino} converter, used as the
   first stage of {F117} and many other Herschel conduits.  There are
   two variants, both shown in the pattern below.
	..........*..............................*..........
	..........***..........................***..........
	.............*........................*.............
	**..........**........................**..........**
	.*................................................*.
	.*.*............................................*.*.
	..**............................................**..
	.....................*........*.....................
	.....................**......**.....................
	......................**....**......................
	......................*......*......................
	.....................*........*.....................
	....................................................
	..*..............................................*..
	..*.*..........................................*.*..
	..***..........................................***..
	....*...........**.................**..........*....
	................*..................**...............
	.................***...................**...........
	...................*...................*............
	........................................***.........
	..........................................*.........

:H-heptomino:  Name given by Conway to the following {heptomino}.  After
   one generation this is the same as the {I-heptomino}.
	**..
	.*..
	.***
	..*.

:high-bandwidth telegraph: (p960, p30 circuitry)  A variant of the
   {telegraph} constructed by Louis-Francois Handfield in February 2017,
   using periodic components to achieve a transmission rate of one bit
   per 192 ticks.  The same ten signals are sent as in the original
   {telegraph} and the {p1 telegraph}, but information is encoded more
   efficiently in the timing of those signals.  Specifically, the new
   transmitter sends five bits every 960 ticks by adjusting the relative
   timings inside each of the five mirror-image paired subunits of the
   composite signal in the beehive-chain {lightspeed wire} {fuse}.

:high-clearance:   See {clearance}.

:highway robber:  Any mechanism that can retrieve a signal from a
   spaceship {lane} while allowing spaceships on nearby lanes to pass by
   unaffected.  In practice the spaceship is generally a glider.  The
   signal is removed from the lane, an output signal is generated
   elsewhere, and the highway robber returns to its original state.  A
   competent highway robber does not affect gliders even on the lane
   adjacent to the affected glider stream, except during its recovery
   period.
     A perfect highway robber doesn't affect later gliders even in the
   lane to which it is attached, even during its recovery period.  Below
   is a near-perfect highway robber "bait" that requires three
   {synchronized} signals to rebuild (the {Herschel}, {B-heptomino}, and
   {glider}.)  The glider at the top right passes by unharmed, but
   another glider following on the same {lane} 200 ticks later will be
   cleanly reflected to a new path, and another glider following that
   one will also pass by unharmed.  The only imperfection is a few ticks
   at the very end of the reconstruction, as the beehive is being
   rebuilt:
	......................*...........*.........
	......................***.......*.*.........
	.........**...**.........*.......**.........
	.........**...**........**..................
	............................................
	............................................
	..**........................................
	...*........................................
	...*.*......................................
	....**......................................
	............................................
	............................................
	............................................
	............................................
	............................................
	............................................
	.......**...................................
	........*...................................
	.....***....................................
	.....*......................................
	............................................
	............................................
	............................................
	............................................
	............................................
	............................................
	....................**......................
	....................**......................
	............**..............................
	.............*..............................
	*.........***...............................
	***.......*.................................
	...*........................................
	..**........................................
	............................................
	............................................
	............................................
	............................................
	...........*...........**...............**..
	.........***..........*.*...............**..
	.........*.*............*...................
	.........*.....................**.*.......*.
	...............................*.**......***
	........................................**.*
	............................................
	.............................**.............
	.............................**.............
	.......................**...................
	.......................**...................
	............................................
	............................................
	.........................**.................
	..................**.....**.................
	..................**........................

:hive:  = {beehive}

:hivenudger: (c/2 orthogonally, p4)  A {spaceship} found by Hartmut
   Holzwart in July 1992.  (The name is due to Bill Gosper.)  It
   consists of a {pre-beehive} escorted by four {LWSS}.  In fact any
   LWSS can be replaced by a {MWSS} or an {HWSS}, so that there are 45
   different single-hive hivenudgers.
	****.....*..*
	*...*...*....
	*.......*...*
	.*..*...****.
	.............
	.....**......
	.....**......
	.....**......
	.............
	.*..*...****.
	*.......*...*
	*...*...*....
	****.....*..*
   Wider versions can be made by stabilizing the front of the extended
   "pre-beehive", as in the {line puffer} shown below.
	.........*.*..................
	........*..*..................
	.......**.....................
	......*...*...................
	.....***.*....................
	..**..........................
	.*...*****.......****.....*..*
	*...*............*...*...*....
	*.....**.........*.......*...*
	***...****........*..*...****.
	.*.......*....................
	.**...................**......
	.*.*..................**......
	.**..**.*........*.*..**......
	..*.***.*...*.****.*..**......
	.........**.*.**..*...**...***
	....******.**...****..**...***
	.....*....***......*..**...***
	......**.....**..**...**......
	.......*..*.....****..**......
	........*.*.**.....*..**......
	......................**......
	..............................
	..................*..*...****.
	.................*.......*...*
	.................*...*...*....
	.................****.....*..*

:honey bit:  A block and pond {constellation} used in the
   {OTCA metapixel} by Brice Due in 2006, to store and retrieve a bit of
   data - specifically, the presence or absence of a neighbor
   {metacell}.  The "0" state of the honey bit memory unit is a simple
   {beehive}, which is also the source of the name.
     An input glider collides with the beehive to convert it into the
   honey bit constellation, which can be thought of as a value of "1"
   stored in the memory unit.  A passing LWSS can then test for the
   presence of the pond.  If a collision occurs, the LWSS and the honey
   bit constellation are mutually annihilated, leaving just the original
   beehive.  Below is the honeybit constellation with the two reactions
   occurring in the opposite order - test, then reset.
	.*...............
	..*..............
	***..............
	.................
	............****.
	............*...*
	............*....
	.............*..*
	.................
	..........**.....
	.........*..*....
	.........*..*....
	..........**.....
	.................
	.................
	.........**......
	.........**......
   If the pond is not present, the LWSS passes by the beehive without
   affecting it.  Thus a test input has an output for the "0" case, but
   not for the "1" case.  For an alternative memory-unit mechanism with
   both "0" and "1" outputs, see {demultiplexer}.
     The honey bit is also an interesting {eater} for the {HWSS} as
   shown below.  An HWSS colliding with the pond happens to create the
   exact same reset glider used in the above memory unit.
	..**...........
	*....*......**.
	......*....*..*
	*.....*....*..*
	.******.....**.
	...............
	...............
	...........**..
	...........**..

:honeycomb: (p1)
	..**..
	.*..*.
	*.**.*
	.*..*.
	..**..

:honey farm: (p1)  A common formation of four beehives.
	......*......
	.....*.*.....
	.....*.*.....
	......*......
	.............
	.**.......**.
	*..*.....*..*
	.**.......**.
	.............
	......*......
	.....*.*.....
	.....*.*.....
	......*......

:hook:  Another term for a {bookend}.  It is also used for other
   hook-shaped things, such as occur in the {eater1} and the
   {hook with tail}, for example.

:hook with tail: (p1)  For a long time this was the smallest
   {still life} without a well-established name.  It is now a vital
   component of the smallest known {HWSS} {gun}, where it acts as a
   {rock}.
	*.*..
	**.*.
	...*.
	...**

:houndstooth agar:  The p2 {agar} that results from tiling the plane
   with the following pattern.
	.***
	.*..
	..*.
	***.

:house:  The following {induction coil}.  It is generation 3 of the
   {pi-heptomino}.  See {spark coil} and {dead spark coil}.
	.***.
	*...*
	**.**

:H-to-G:  A {Herschel-to-glider} {converter}.

:H-to-MWSS:  A {Spartan} {converter} found by Tanner Jacobi in October
   2015, which converts an input {Herschel} to a middleweight spaceship.
   The key discovery was a very small but slightly {dirty} H-to-MWSS
   conduit, where a Herschel is catalyzed to produce an {MWSS} but also
   leaves behind a beehive.  Prefixing two {R64} conduits to this
   produces a {composite} converter that successfully deletes the
   beehive in advance, using the input Herschel's
   {first natural glider}.
	.............................**................
	.............................**.....**.........
	....................................**.........
	...............................................
	...............................................
	...............**.................**...........
	................*.................**...........
	................*.*.....................**.....
	.................**.....................**.....
	...............................................
	...............................................
	...............................................
	....................*..........................
	....................*.*........................
	....................***........................
	......................*........................
	...............................................
	...............................................
	...............................................
	...............................................
	...............................................
	...............................................
	...**...........................***............
	..*.*...........................*..............
	...*...........................**..............
	...............................................
	...............................................
	...............................................
	...............................................
	...............................................
	...............................................
	.............................................**
	.*...........................................**
	*.*................**.*........................
	*.*................**.***......................
	.*......................*......................
	........................*...............**.....
	........................................**.....
	....*.*.....................................**.
	.......*....................................**.
	...*...*.......................................
	.......*.......................................
	....*..*..............................**.......
	.....***..............................**.......
   There are many other ways to remove the beehive using a spare glider
   or additional conduits, but they are generally less compact than
   this.

:hustler: (p3)  Found by Robert Wainwright, June 1971.
	.....**....
	.....**....
	...........
	...****....
	*.*....*...
	**.*...*...
	...*...*.**
	...*....*.*
	....****...
	...........
	....**.....
	....**.....

:hustler II: (p4)
	....*...........
	....***.........
	.......*........
	......*..**.....
	*.**.*.**..*....
	**.*.*.....*....
	.....*....*.....
	....*.....*.*.**
	....*..**.*.**.*
	.....**..*......
	........*.......
	.........***....
	...........*....

:HW emulator: (p4)  Found by Robert Wainwright in June 1980.  See also
   {emulator}.
	.......**.......
	..**.*....*.**..
	..*..........*..
	...**......**...
	***..******..***
	*..*........*..*
	.**..........**.

:HWSS: (c/2 orthogonally, p4)  A heavyweight spaceship, the fourth most
   common {spaceship}.  Found by Conway in 1970 by modifying a {LWSS}.
   See also {MWSS}.
	...**..
	.*....*
	*......
	*.....*
	******.
     The HWSS possesses both a {tail spark} and a {domino} {belly spark}
   which can easily perturb other objects as it passes by.  The
   spaceship can also perturb some objects in additional ways.  For
   examples, see {puffer} and {glider turner}.
     Dave Buckingham found that the HWSS can be synthesized using three
   gliders as shown below:
	........*.*
	........**.
	.........*.
	...........
	***........
	..*........
	.*...***...
	.......*...
	......*....

:HWSS emulator:  = {HW emulator}

:HW volcano: (p5)  A p5 {domino} {sparker}, found by Dean Hickerson in
   February 1995.
	.........*..........................
	........*.*.........................
	......***.*.........................
	.....*....**.*......................
	.....*.**...**......**..............
	....**.*.**.........*.*.............
	.........*.*****......*..*.**.......
	..*.**.**.*.....*....**.*.**.*......
	.....**.....****........*....*......
	*...*.*..*...*.*....**.*.****.**....
	*...*.*..**.*.**.**....*.*....*.*...
	.....**...***.**.*.***.*..***...*...
	..*.**.**.**.............*.*..*.*.**
	...........*......*.*.*.*..**.*.*.*.
	....**.*.*.**......**.*.*.*...*.*.*.
	.....*.**.*..*.......*.**..****.**..
	.....*....*.*........*...**.........
	....**....**........**...*..*.......
	...........................**.......
   At least four progressively smaller forms of this sparker have been
   found, including a 25-cell-wide version found by David Eppstein in
   2003, and a vertically narrower 28-cell-wide version by Karel Suhajda
   in 2004.  Scot Ellison's 17-cell-wide version is shown in the
   {zweiback} entry.

:hybrid grey ship:  A {grey ship} containing more than one type of
   region of density 1/2, usually a combination of a
   {with-the-grain grey ship} and an {against-the-grain grey ship}.

:I-heptomino:  Name given by Conway to the following {heptomino}.  After
   one generation this is the same as the {H-heptomino}.
	**..
	.*..
	.**.
	..**

:IMG:  = {intermitting glider gun}

:Immigration:  A form of {colourised Life} in which there are two types
   of ON cell, a newly-born cell taking the type of the majority of its
   three {parent cells} and surviving cells remaining of the same type
   as in the previous generation.

:independent conduit:  A {Herschel conduit} in which the input Herschel
   produces its {first natural glider}.  Compare {dependent conduit}.

:induction coil:  Any object used to stabilize an edge (or edges)
   without touching.  The tubs used in the {Gray counter} are examples,
   as are the blocks and snakes used in the {Hertz oscillator} and the
   heptomino at the bottom of the {mathematician}.

:inductor:  Any {oscillator} with a row of dead cells down the middle
   and whose two halves are mirror images of one another, both halves
   being required for the oscillator to work.  The classic examples are
   the {pulsar} and the {tumbler}.  If still lifes are considered as p1
   oscillators then there are numerous simple examples that include this
   kind of central {gutter}, such as {table on table}, {dead spark coil}
   and {cis-mirrored R-bee}. Some spaceships, such as the {brain}, the
   {snail} and the {spider}, use the same principle.

:infinite glider hotel:  A pattern by David Bell, named after Hilbert's
   "infinite hotel" scenario in which a hotel with an infinite number of
   rooms has room for more guests even if it is already full, simply by
   shuffling the old guests around.
     In this pattern, two pairs of {Cordership}s moving at c/12 are
   pulling apart such that there is an ever-lengthening {glider} track
   between them.  Every 128 generations another glider is {inject}ed
   into the glider track (see {LWSS-glider bounce}), joining the gliders
   already circulating there. The number of gliders in the track
   therefore increases without limit.
     The tricky part of this construction is that even though all the
   previously injected gliders are repeatedly flying through the
   injection point, that point is guaranteed to be empty when it is time
   for the next glider to be injected.

:infinite growth:  Growth of a finite pattern such that the {population}
   tends to infinity, or at least is unbounded. Sometimes the term is
   used for growth of something other than population (for example,
   length), but here we will only consider infinite population growth.
   The first known pattern with infinite growth in this sense was the
   {Gosper glider gun}, created in a response to a $50 prize challenge
   by John Conway.  Martin Gardner's October 1970 article described the
   challenge as "Conway conjectures that no pattern can grow without
   limit", but Conway later explained that he had always expected that
   this would be disproved.  The original purpose in investigating CA
   rules including B3/S23 was to show that a very simple two-state rule
   could support a {universal computer} and/or {universal constructor}.
   If all finite patterns could be proven to be bounded, neither of
   these would be possible.
     An interesting question is: What is the minimum population of a
   pattern that exhibits infinite growth?  In 1971 Charles Corderman
   found that a {switch engine} could be stabilized by a {pre-block} in
   a number of different ways, giving 11-cell patterns with infinite
   growth.  This record stood for more than quarter of a century until
   Paul Callahan found, in November 1997, two 10-cell patterns with
   infinite growth.  The following month he found the one shown below,
   which is much neater, being a single {cluster}. This produces a
   stabilized switch engine of the block-laying type.
	......*.
	....*.**
	....*.*.
	....*...
	..*.....
	*.*.....
   Nick Gotts and Paul Callahan showed in October 1997 that there is no
   infinite growth pattern with fewer than 10 cells, so that question
   has now been answered.
     In October 2014, Michael Simkin discovered a three-glider collision
   that produces a glider-producing {stabilized switch engine} and thus
   produces infinite growth from the smallest possible number of gliders
   (since all 71 {2-glider collision}s have a finite limit population).
     Also of interest is the following pattern (again found by
   Callahan), which is the only 5x5 pattern with infinite growth. This
   too emits a block-laying switch engine.
	***.*
	*....
	...**
	.**.*
	*.*.*
     Following a conjecture of Nick Gotts, Stephen Silver produced, in
   May 1998, a pattern of width 1 which exhibits infinite growth.  This
   pattern was very large (12470x1 in the first version, reduced to
   5447x1 the following day).  In October 1998 Paul Callahan did an
   exhaustive search, finding the smallest example, the 39x1 pattern
   shown below.  This produces two block-laying switch engines,
   stability being achieved at generation 1483.
	********.*****...***......*******.*****
   Larger patterns have since been constructed that display
   {quadratic growth}.
     Although the simplest infinite growth patterns grow at a rate that
   is (asymptotically) linear, many other types of growth rate are
   possible, {quadratic growth} (see also {breeder}) being the fastest.
   Dean Hickerson has found many patterns with unusual growth rates,
   such as {sawtooth}s and a {caber tosser}.  Another pattern with
   superlinear but non-quadratic growth is {Gotts dots}.
     See also {Fermat prime calculator}.

:initials:  = {monogram}

:inject:  A reaction in which a hole in a regular spaceship stream is
   filled partially or fully by adding a new spaceship of the same type
   without affecting the existing spaceships in the stream.  Depending
   on the period of the stream, different mechanisms can be used.  For
   adding a spaceship to an existing multi-lane {convoy}, see
   {inserter}.
     For large period glider streams, simple reactions such as
   {LWSS-LWSS bounce} and {LWSS-glider bounce} suffice.  If {Herschel}
   technology is used, a large number of {edge shooter}s and
   {transparent} conduits are known.  Simple examples include the {NW31}
   {Herschel-to-glider} {converter} and the {Fx119 inserter}.
     Shown below is an injector found by Dave Buckingham that can fill a
   hole in a p15 glider stream:
	..*.*..................
	...**..................
	...*.................*.
	....................*..
	....................***
	.......................
	.......................
	..........*............
	...........**..........
	..........**...........
	.......................
	.**....................
	*.*..**................
	..*.**.................
	......*................
	.......................
	.......................
	.......................
	.....**................
	......**...............
	.....*.................
   For very low-period glider streams, a {GIG} is a much more efficient
   insertion method, in the sense that fewer {synchronized} {signal}s
   are needed.  However, it has been shown that colliding gliders can
   complete an insertion even into a single-glider gap in a period-14
   stream.

:inline inverter:  The following reaction in which a p30 {gun} can be
   used to invert the presence or absence of gliders in a p30 stream,
   with the output glider stream being in the same direction as the
   input glider stream.
	................*...................
	.................*..................
	...............***..................
	....................................
	.......................*.*..........
	.....................*...*..........
	.............*.......*..............
	............****....*....*........**
	...........**.*.*....*............**
	**........***.*..*...*...*..........
	**.........**.*.*......*.*..........
	............****....................
	.............*......................

:inserter:  A mechanism that can add another spaceship into a stream or
   convoy of other spaceships without affecting the existing spaceships.
   For examples see {Fx119 inserter}, {tee}, {GIG}, {clock insertion}
   and {inject}.

:integral:  = {integral sign}

:integral sign: (p1)
	...**
	..*.*
	..*..
	*.*..
	**...

:intentionless:  = {elevener}

:interchange: (p2)  A common formation of six blinkers.
	..***....***..
	..............
	*............*
	*............*
	*............*
	..............
	..***....***..

:intermediate target:  A temporary product of a partial {slow salvo},
   {elbow operation}, or {glider synthesis}.  An intermediate target is
   a useful step toward a desired outcome, but will not appear in the
   final construction.

:intermittent stream:  A {stream} of spaceships which is based on a
   periodic stream, but which can contain holes where some of the
   spaceships are not present. There is a base period for the
   intermittent stream such that if a spaceship arrives at a specific
   location, then it always does so at a generation which is a multiple
   of the base period.  For example, the output from a period 30 glider
   gun where every third glider is deleted is an intermittent stream.  A
   {pseudo-random glider generator} can produce a complicated
   intermittent stream with no obvious pattern.
     Intermittent streams can be used to transmit {signal}s, where holes
   in the stream can also convey information.  For example, the stream
   can be processed by an {inverter} having the same period.

:intermitting glider gun:  Despite the name, an intermitting glider gun
   (IMG) is more often an {oscillator} than a {gun}.  There are two
   basic types.  A type 1 IMG consists of two guns firing at one another
   in such a way that each gun is temporarily disabled on being hit by a
   glider from the other gun.  A type 2 IMG consists of a single gun
   firing at a 180-degree glider {reflector} in such a way that
   returning gliders temporarily disable the gun.
     Both types of IMG can be used to make glider guns of periods that
   are multiples of the base period.  This is done by firing another gun
   across the two-way {intermittent stream} of gliders in the IMG in
   such a way that gliders only occasionally escape.

:inverter:  A device which can be used to invert the presence or absence
   of spaceships in an {intermittent stream} of spaceships.  The device
   must be a gun whose period matches the base period of the stream,
   since if there are no input spaceships then the device must produce
   spaceships as the result of the inversion.  Typically the spaceships
   are gliders, and the inverter is made from a glider gun.  Inverters
   provide a way to produce a NOT logic operation on a stream.
     There are several ways to produce an inverter.  The simplest method
   is to simply hit the output of a gun with the input stream to delete
   its spaceships, producing an output stream that is always turned 90
   degrees from the input stream.  An example is the northernmost p30
   gun in the {glider duplicator} example pattern.  For one way to
   produce an inverted output stream which is not turned, see
   {inline inverter}.

:inverting reflector:  See {inverter}.

:island:  The individual {polyplet}s of which a {stable} pattern
   consists are sometimes called islands.  So, for example, a {boat} has
   only one island, while an {aircraft carrier} has two, a {honey farm}
   has four and the standard form of the {eater3} has five.

:Iwona: (stabilizes at time 28786)  The following {methuselah} found by
   Andrzej Okrasinski in August 2004.
	..............***...
	....................
	....................
	....................
	....................
	....................
	..*.................
	...**...............
	...*..............*.
	..................*.
	..................*.
	...................*
	..................**
	.......**...........
	........*...........
	....................
	....................
	....................
	....................
	**..................
	.*..................
   It has a final population of 3091 and covers an area of 413 by 364
   cells, not counting the 47 gliders it produces.  Its {ash} consists
   of typical stable objects and blinkers, along with the relatively
   rare {paperclip}.

:J:  = {Herschel}

:jack: (p4)  Found by Robert Wainwright, April 1984.
	...*.....*...
	...**...**...
	*..**...**..*
	***..*.*..***
	.....*.*.....
	***..*.*..***
	*..**...**..*
	...**...**...
	...*.....*...

:jagged lines:  A pattern constructed by Dean Hickerson in May 2005 that
   uses {puffer}s to produce a line of {bi-block}s that weaves back and
   forth in a complicated way.

:jam: (p3)  Found by Achim Flammenkamp in 1988, but not widely known
   about until its independent discovery (and naming) by Dean Hickerson
   in September 1989.  Compare with {mold}.  In fact this is really very
   like {caterer}.  In terms of its 7x7 {bounding box} it ties with
   {trice tongs} as the smallest p3 {oscillator}.
	...**.
	..*..*
	*..*.*
	*...*.
	*.....
	...*..
	.**...

:JavaLifeSearch:  See {lifesrc}.

:Jaws:  A {breeder} constructed by Nick Gotts in February 1997.  In the
   original version Jaws had an initial {population} of 150, which at
   the time was the smallest for any known pattern with
   {superlinear growth}.  In November 1997 Gotts produced a 130-cell
   Jaws using some {switch engine} {predecessor}s found by Paul
   Callahan.  See {switch-engine ping-pong} for the lowest-population
   superlinear growth pattern as of July 2018, along with a list of the
   record-holders.
     Jaws consists of eight pairs of switch engines which produce a new
   block-laying switch engine (plus masses of junk) every 10752
   generations.  It is therefore an MMS breeder.

:JC:  = {dead spark coil}

:JHC:  John Horton Conway.  Also another name for {monogram}.

:J-heptomino:  = {Herschel}

:JLS:  = {JavaLifeSearch}

:Jolson: (p15)  Two {block}s {hassle}d by two {pentadecathlon}s. Found
   by Robert Wainwright in November 1984 and named by Bill Gosper.  A p9
   version using {snacker}s instead of pentadecathlons is also possible.
	.**......**..
	*..*....*..*.
	*..*....*..*.
	*..*....*..*.
	.**......**..
	.............
	.............
	.......*.....
	.....*..*.**.
	......**..**.
	.............
	.............
	......****...
	.....******..
	....********.
	...**......**
	....********.
	.....******..
	......****...

:junk:  = {ash}.

:Justyna: (stabilizes at time 26458)  The following {methuselah} found
   by Andrzej Okrasinski in May 2004.
	.................*....
	................*..*..
	.................***..
	.................*..*.
	......................
	**................*...
	.*................*...
	..................*...
	......................
	......................
	......................
	......................
	......................
	......................
	......................
	...................***
	...........***........

:Karel's p15: (p15)  An {oscillator} discovered by Karel Suhajda on
   December 11, 2002.  It consists of a period 15 rotor supported by the
   domino spark of a pentadecathlon. It provides accessible sparks that
   can be used to perturb reactions or thin signal {stream}s.
	..*....*..
	..******..
	..*....*..
	..........
	..........
	..........
	..******..
	.*......*.
	*........*
	.*......*.
	..******..

:keeper:  A type of {factory} {circuit} that always results in the
   presence of an object in the output location, whether or not the
   object was previously present.  In many cases it is easy to construct
   examples by connecting multiple circuits to shoot down an object with
   a {glider}, then rebuild the object again later.  The smallest keeper
   circuits accomplish the same thing more directly with a lucky
   preliminary {spark} from the active reaction, which removes the
   existing object (if any) just before the construction occurs.  Below
   is a useful block keeper with a {Herschel} input.
	................*..............................
	................***.....**.....................
	...................*....**.....................
	..................**...........................
	...............................................
	...............................................
	...............................................
	...............................................
	...............................................
	................................**.............
	...............................*.*.............
	................................*..............
	...............................................
	...............................................
	.......**......................................
	........*......................................
	........*.*....................................
	.........**....................................
	...............................................
	...............................................
	...............................................
	...............................................
	...............................................
	...............................................
	.........*...................................**
	.........*.*.................................**
	.........***...................................
	...........*...................................
	...............................................
	...............................................
	..........................**...................
	..........................**...................
	..**...........................................
	...*...........................................
	***.........**.................................
	*...........**.................................

:keys:  See {short keys}, {bent keys} and {odd keys}.

:kickback:  = {kickback reaction} or {180-degree kickback}.

:kickback reaction:  The following collision of two {glider}s whose
   product is a single glider travelling in the opposite direction to
   one of the original gliders.  This is important in the proof of the
   existence of a {universal constructor}, and in Bill Gosper's
   {total aperiodic}, as well as a number of other constructions.
	.....*..
	......**
	.**..**.
	*.*.....
	..*.....
   See also {180-degree kickback}.

:kidney:  A Gosperism for {century}.  See also {diuresis}.

:killer toads:  A pair of {toad}s acting together so that they can eat
   things.  Here, for example, are some killer toads eating an {HWSS}.
   Similarly they can eat a {MWSS} (but not a {LWSS}).  For another
   example see {twirling T-tetsons II}.  See also {candlefrobra}.
	..**.......***
	*....*....***.
	......*.......
	*.....*.......
	.******.......
	..........***.
	...........***

:Klein bottle:  As an alternative to a {torus}, it's possible to make a
   finite Life universe in the form of a Klein bottle.  The simplest way
   to do this is to use an m x n rectangle with the top edge joined to
   the bottom edge (as for a torus) and the left edge twisted and joined
   to the right.

:knightship:  Any {spaceship} of type (2m,m)/n - that is, a spaceship of
   any speed that moves obliquely in a (2,1) direction.  The first
   Conway's Life knightship was a variant of Andrew Wade's {Gemini}
   spaceship, constructed in May 2010.  The next was an even slower
   knightship based on the {half-bakery reaction}.
     A knightship must be asymmetric and its period must be at least 6.
   This is barely within the range of current {search program}s, as
   proven by the discovery on March 6, 2018 of an {elementary}
   knightship, {Sir Robin}, by Adam P. Goucher and Tomas Rokicki.
     By analogy with the corresponding fairy chess pieces, spaceships of
   types (3m,m)/n, (3m,2m)/n and (4m,m)/n would presumably be called
   camelships, zebraships and giraffeships, respectively.  Such
   spaceships do exist (see {universal constructor}) but small
   elementary versions are even more difficult to search for.  Any of
   these ship types could be constructed by trivially modifying a Gemini
   spaceship, or less trivially by reprogramming one of the more recent
   small {Geminoid} {construction arm}s, but as of July 2018 a camelship
   Gemini is the only example that has been explicitly built.
     Alternatively, the term "knightship" is regularly used to refer to
   any {oblique} spaceship, such as the original {Gemini} or the
   {waterbear}.

:Kok's galaxy: (p8)  An {oscillator} found by Jan Kok in 1971, currently
   serving as the icon for {Golly}.  See {converter} for a use of this
   {sparker}.
	******.**
	******.**
	.......**
	**.....**
	**.....**
	**.....**
	**.......
	**.******
	**.******

:L112:  A {composite conduit}, one of the original sixteen
   {Herschel conduit}s, discovered by Dave Buckingham in July 1996.  It
   is made up of two {elementary conduit}s, HLx53B +  {BFx59H}.  After
   112 ticks, it produces a {Herschel} turned 90 degrees
   counterclockwise at (12, -33) relative to the input.  Its
   {recovery time} is 61 ticks; this can be reduced slightly by removing
   the output glider, either with a specialized eater (as in the
   original {true} p59 gun), or with a {sparker} as in most of the
   {Quetzal} guns.  It can be made {Spartan} by replacing the
   {aircraft carrier} with an {eater1}.  A {ghost Herschel} in the
   pattern below marks the output location:
	...............**.......
	...............*........
	.............***........
	........................
	........................
	........................
	........................
	........................
	........................
	........................
	........................
	........................
	........................
	........................
	........................
	........................
	........................
	........................
	.............**.........
	.............**.........
	....**..................
	....*..*................
	**....**................
	.*....................**
	.*.*..................*.
	..**................*.*.
	....................**..
	........................
	........................
	........................
	........................
	........................
	..*.....................
	..*.*...................
	..***...................
	....*...................
	........................
	..............**........
	..............**..**....
	..................*.*...
	....................*...
	....................**..

:L156:  A {composite conduit}, one of the original sixteen
   {Herschel conduit}s, discovered by Dave Buckingham in August 1996.
   It is made up of three {elementary conduit}s, HLx69R + {RF28B} +
   {BFx59H}.  After 156 ticks, it produces a {Herschel} turned 90
   degrees counterclockwise at (17, -41) relative to the input.  Its
   {recovery time} is 62 ticks.  It can be made {Spartan} by replacing
   the {snake} with an {eater1} in one of two orientations.  Additional
   gliders can be produced by removing the southeasternmost eater, or by
   replacing the RF28B elementary conduit by an alternate version.  A
   {ghost Herschel} in the pattern below marks the output location:
	...................**........
	...................*.........
	.................***.........
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.................**..........
	.................**..........
	.............................
	........**.*.................
	........*.**.................
	..........................**.
	..........................*..
	........................*.*..
	........................**...
	.............................
	.........*...................
	.........***.................
	*...........*................
	***........**..............*.
	...*......................*.*
	..**.......................*.
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.*....................**.....
	.*.*..................*.*....
	.***....................*....
	...*...........**.......**...
	...............*.............
	................***..........
	..................*..........

:lake: (p1)   Any still life consisting of a simple closed curve made
   from diagonally connected {domino}es.  The smallest example is the
   {pond}, and the next smallest is this (to which the term is sometimes
   restricted):
	....**....
	...*..*...
	...*..*...
	.**....**.
	*........*
	*........*
	.**....**.
	...*..*...
	...*..*...
	....**....

:lane:  A path traveled by a glider, or less commonly a spaceship such
   as a loafer.  The lane is centered on the line of symmetry (if any)
   of the spaceship in question.  If a lane is clear, then the spaceship
   can travel along it without colliding or interfering with any other
   objects.
     Diagonal lanes are often numbered consecutively, in half-diagonals
   ({hd}).  Occasionally diagonal lane measurements are given in
   quarter-diagonals ({qd}), in part because diagonally symmetric
   spaceships have a line of symmetry 1qd away from the lines available
   for gliders.  It's also convenient that moving a glider forward by
   100qd (for example) has the same effect as evolving the same glider
   for 100 ticks.

:Laputa: (p2)  Found by Rich Schroeppel, September 1992.
	...**.**....
	...**.*...**
	........*..*
	.******.***.
	*..*.*......
	**...*.**...
	....**.**...

:large prime oscillator:  Any oscillator with a relatively small
   {bounding box} whose period is a very large prime.  (If the
   bounding-box restriction is removed, then eight gliders travelling in
   a four-{Snark} loop would provide a trivial example for any chosen
   prime.)  The first such oscillator was built by Gabriel Nivasch in
   2003.  The current record holder is an oscillator constructed by Adam
   P. Goucher with a period that is a Mersenne prime with 13,395 digits
   (2^44497-1).
     The next higher Mersenne-prime oscillator, period 2^86243-1, could
   be constructed with {quadri-Snark}s and {semi-Snark}s.  It would
   actually be significantly smaller than the current record holder.  As
   of June 2018 the construction of this pattern has not yet been
   completed.

:large S:  = {big S}

:Lidka: (stabilizes at time 29053)  A {methuselah} found by Andrzej
   Okrasinski in July 2005.
	..........***..
	..........*....
	..........*...*
	...........*..*
	............***
	...............
	.*.............
	*.*............
	.*.............
   The following variant, pointed out by David Bell, has two fewer cells
   and lasts two generations longer.
	..........***..
	...............
	...........**.*
	............*.*
	..............*
	...............
	.*.............
	*.*............
	.*.............

:Life:  A 2-dimensional 2-state {cellular automaton} discovered by John
   Conway in 1970.  The states are referred to as ON and OFF (or live
   and dead).  The transition rule is as follows: a cell that is ON will
   remain ON in the next generation if and only if exactly 2 or 3 of the
   8 adjacent cells are also ON, and a cell that is OFF will turn ON if
   and only if exactly 3 of the 8 adjacent cells are ON.  (This is more
   succinctly stated as: "If 2 of your 8 nearest neighbours are ON,
   don't change.  If 3 are ON, turn ON.  Otherwise, turn OFF.")

:Life32:  A freeware Life program by Johan Bontes for Microsoft Windows
   95/98/ME/NT/2000/XP: {https://github.com/JBontes/Life32/}.

:LifeHistory:  A multistate CA rule supported by {Golly}, equivalent to
   two-state B3/S23 Life but with several additional states intended for
   annotation purposes.  A "history" state records whether an off cell
   has ever turned on in the past, and other states allow on and off
   cells to be permanently or temporarily marked, without affecting the
   {evolution} of the pattern.

:LifeLab:  A shareware Life program by Andrew Trevorrow for the
   Macintosh (MacOS 8.6 or later): {http://www.trevorrow.com/lifelab/}.

:LifeLine:  A newsletter edited by Robert Wainwright from 1971 to 1973.
   During this period it was the main forum for discussions about Life.
   The newsletter was nominally quarterly, but the actual dates of its
   eleven issues were as follows:
	Mar, Jun, Sep, Dec 1971
	Sep, Oct, Nov, Dec 1972
	Mar, Jun, Sep 1973

:Lifenthusiast:  A Life enthusiast.  Term coined by Robert Wainwright.

:lifesrc:  David Bell's Life {search program} for finding new
   {spaceship}s and {oscillator}s.  This is a C implementation of an
   algorithm developed by Dean Hickerson in 6502 assembler.
     Although lifesrc itself is a command-line program, Jason Summers
   has made a GUI version called {WinLifeSearch} for Microsoft Windows.
   A Java version, {JavaLifeSearch}, was written in November 2012 by
   Karel Suhajda.
     The lifesrc algorithm is only useful for very small periods, as the
   amount of computing power required rises rapidly with increasing
   period.  For most purposes, period 7 is the practical limit with
   current hardware.
     Lifesrc is available from {http://tip.net.au/~dbell/} (source code
   only).  Compare {gfind}.

:LifeViewer:  A scriptable Javascript Life pattern viewer written by
   Chris Rowett, used primarily on the conwaylife.com discussion forums.

:light bulb: (p2)  Found in 1971.
	.**.*..
	.*.**..
	.......
	..***..
	.*...*.
	.*...*.
	..*.*..
	*.*.*.*
	**...**
   The same {rotor} can be embedded in a slightly smaller {stator} like
   this:
	...*.....
	.***.....
	*........
	******...
	......*..
	..*...*..
	..**.*...
	......***
	........*

:lightspeed bubble:  A type of {negative spaceship} travelling through
   the {zebra stripes} agar.  The center of the bubble is simple empty
   space, and the length and/or width of the bubble can usually be
   extended to any desired size.
     Below is a small stabilized section of agar containing a sample
   lightspeed bubble, found by Gabriel Nivasch in August 1999.  The
   bubble travels to the left at the {speed of light}, so it will
   eventually reach the edge of any finite patch and destroy itself and
   its supporting agar.
	.*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*...
	.************************************************************.
	.............................................................*
	.*************..***..***..***********************************.
	*..............**...**...**........*..........................
	.*************...**...**...*.**.*....************************.
	.............................**.....*........................*
	.*************.................******************************.
	*...............................*.............................
	.*************...................****************************.
	.................................*....*......................*
	.*************...................**....**********************.
	*................................*.....*....*.................
	.*************...................**....**....****************.
	.................................*.....*.....*....*..........*
	.*************...................**....**....**....**********.
	*................................*.....*.....*.....*....*.....
	.*************...................**....**....**....**....****.
	.................................*.....*.....*.....*.....*...*
	.*************...................**....**....**....**....****.
	*................................*.....*.....*.....*....*.....
	.*************...................**....**....**....**********.
	.................................*.....*.....*....*..........*
	.*************...................**....**....****************.
	*................................*.....*....*.................
	.*************...................**....**********************.
	.................................*....*......................*
	.*************...................****************************.
	*...............................*.............................
	.*************.................******************************.
	.............................**.....*........................*
	.*************...**...**...*.**.*....************************.
	*..............**...**...**........*..........................
	.*************..***..***..***********************************.
	.............................................................*
	.************************************************************.
	.*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*...
     An open problem related to lightspeed bubbles was whether large
   extensible empty areas could be created whose length was not
   proportional to the width (as it must be in the above case, due to
   the tapering back edge).  This was solved in February 2017 by Arie
   Paap; a simple period-2 solution is shown below.
	...*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*...
	.***********************************************************.
	*...........................................................*
	.***********************************************************.
	.............................................................
	.***********************************************************.
	*.....................................................*.....*
	.********************..***..***..***..********..****...*****.
	......................**...**...**...**........**.....*......
	.********************...**...**...**...*******...*.**..*****.
	*.........................................*........**.......*
	.********************......................**.*......*******.
	...........................................*............*....
	.********************......................*.............***.
	*..........................................**.....**....*...*
	.********************......................**...**...*.*****.
	...........................................*..*.**...*.......
	.********************......................*......**...*****.
	*..........................................**..........*....*
	.********************......................**..........*****.
	...........................................*......**.*.......
	.********************......................*..*.**...*.*****.
	*..........................................**...**......*...*
	.********************......................**.....**.....***.
	...........................................*............*....
	.********************......................*...........*****.
	*..........................................**.....**.**.....*
	.********************......................**...**...**..***.
	...........................................*..*.**.....**....
	.********************......................*......**....****.
	*..........................................**...............*
	.********************......................**...........****.
	...........................................*......**...**....
	.********************......................*..*.**...**..***.
	*..........................................**...**...**.....*
	.********************......................**.....**...*****.
	...........................................*............*....
	.**********************.....*.....*.....*..*.*...........***.
	*.........................**....**....**...*...*.*.......*..*
	.************************.**.**.**.**.**.*********.......***.
	........................................................*....
	.*************************************************...*******.
	*..................................................**.......*
	.*************************************************..********.
	.............................................................
	.***********************************************************.
	*...........................................................*
	.***********************************************************.
	...*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*...

:lightspeed ribbon:  = {superstring}

:lightspeed telegraph:  = {telegraph}.

:lightspeed wire:  Any {wick} that can {burn} non-destructively at the
   speed of light.  Lightspeed wires are a type of {reburnable fuse}.
   These are potentially useful for various things, but so far the
   necessary mechanisms are very large and unwieldy.  In October 2002,
   Jason Summers discovered a lightspeed reaction travelling through an
   orthogonal chain of beehives.  Summers completed a period-1440
   lightspeed {telegraph} based on this reaction in 2003.
	...*...........................................................
	.*...*.........................................................
	.*....*....**.**...............................................
	*......*...******...**...**...**...**...**...**...**...**...**.
	*......*..*......*.*..*.*..*.*..*.*..*.*..*.*..*.*..*.*..*.*..*
	**.....*...******...**...**...**...**...**...**...**...**...**.
	......*....**.**...............................................
	....*..........................................................
     A {stable} lightspeed {transceiver} mechanism using this same
   signal reaction, the {p1 telegraph}, was constructed by Adam P.
   Goucher in 2010; the bounding boxes of both the {transmitter} and
   {receiver} are over 5000 cells on a side.  A more compact periodic
   {high-bandwidth telegraph} with a much improved transmission rate was
   completed by Louis-Francois Handfield in 2017.
     The following diagram shows an older example of a lightspeed wire,
   with a small defect that travels along it at the speed of light.  As
   of June 2018, no method has been found of creating such a defect in
   the upstream end of this particular stable wire, or of
   non-destructively detecting the arrival of the defect and repairing
   the wire at the downstream end.
	....**..**..**..**..**..**..**..**..**..**..**..**..**....
	....**..**..**..**..**..**..**..**..**..**..**..**..**....
	..........................................................
	..******************************************************..
	.*......*...............................................*.
	*.*****....*********************************************.*
	.*.....*................................................*.
	..******************************************************..
	..........................................................
	....**..**..**..**..**..**..**..**..**..**..**..**..**....
	....**..**..**..**..**..**..**..**..**..**..**..**..**....

:lightweight emulator:  = {LW emulator}

:lightweight spaceship:  = {LWSS}

:lightweight volcano:  = {toaster}

:linear growth:  A growth rate proportional to T, where T is the number
   of ticks that a pattern has been run.  Compare {superlinear growth},
   {quadratic growth}.

:linear propagator:  A self-replicating pattern in which each copy of a
   pattern produces one child that is an exact copy of itself.  The
   child pattern then blocks the parent from any further replication.
   An example was constructed by Dave Greene on 23 November 2013, with a
   construction arm using two glider lanes separated by {9hd}.  By some
   definitions, due to its limited one-dimensional growth pattern, the
   linear propagator is not a true replicator.  Compare
   {quadratic replicator}.

:line crosser:  A pattern which is able to send a signal across an
   infinite diagonal line of live cells without destroying the line.
   David Bell built one in August 2006.  It uses many one-shot period
   44160 {glider gun}s on both sides of the line having the proper
   synchronization to create the reactions shown in
   {line-cutting reaction} and {line-mending reaction}.
     An input glider can arrive at any multiple of 44160 generations to
   first cut the line, then send a glider through the gap, and finally
   mend the line while leaving an output glider on the other side.
     A line crosser whose complete mechanism is on one side of the line
   is theoretically possible, using {single-channel} construction
   methods for example.

:line-cutting reaction:  A reaction that can cut an infinite diagonal
   line of cells, leaving a gap with both ends sealed.  Such a reaction
   is demonstrated below.  In actual use the reaction should be spread
   out so that the incoming {LWSS}es don't conflict.  See
   {line-mending reaction} for a way to mend the gap.
	.........................**.................................
	............**...........*..................................
	..........**.**...........*.................................
	..........****.............*................................
	...........**...............*...............................
	................**...........*..............................
	...............*.*............*.............................
	.................*.............*............................
	................................*...........................
	.................................*..........................
	..................................*.........................
	...................................*........................
	.......................*............*.......................
	......................***............*......................
	......................*.**............*.....................
	*..*...................***.............*....................
	....*..................**...............*...................
	*...*....................................*..................
	.****.....................................*.................
	...........................................*................
	............................................*...............
	.............................................*..............
	...................................**.........*.............
	....................................**.........*............
	...................................*............*...........
	.................................................*..........
	..................................................*.........
	.....................................***...........*........
	....................................*..*............*.......
	.......................................*.............*......
	.......................................*..............*.....
	....................................*.*................*....
	........................................................*...
	.........................................................*.*
	.......***................................................**
	.........*............**......***..........****.............
	........*............*.*........*.........*...*.............
	.......................*.......*..............*.............
	..........................................*..*..............
	............................................................
	............................................................
	............................................................
	....................................................**......
	.....................................................**.....
	....................................................*.......
	............................................................
	........................................................***.
	........................................................*..*
	........................................................*...
	........................................................*...
	.........................................................*.*
	.......................**...................................
	......................*.*...................................
	........................*...................................
	............................................................
	..........................................*.................
	.........................................***................
	.........................................*.**...............
	..........................................***...............
	..........................................**................

:line-mending reaction:  A reaction which can fully mend a sealed gap in
   an infinite diagonal line of cells, such as the one produced by a
   {line-cutting reaction}.  Such a reaction is demonstrated below.  See
   the line cutting reaction for a way of creating the gliders
   travelling parallel to the line.
	...........**.............................................
	...........*..............................................
	............*.............................................
	...*.*.......*............................................
	....**........*...........................................
	....*..........*..........................................
	................*...................................*.....
	.................*................................**......
	..................*................................**.....
	...................*......................................
	....................*.....................................
	.....................*.....................*.*............
	......................*....................**.............
	.......................*....................*.............
	........................*.................................
	.........................*................................
	..........................*...............*...............
	...........................*.............*................
	............................*............***..............
	.............................*............................
	............................**............................
	..........................................................
	..........................................................
	..........................................................
	...........................................*.*............
	...........................................**.......*..*..
	............................................*......*......
	...................................***.............*...*..
	.....................................*.............****...
	....................................*.....................
	.......................................**.................
	.......................................*.*................
	..........................................*...............
	...........................................*..............
	...............................**...........*.............
	..............................*.*............*............
	................................*.............*.......**..
	.............*..........................**.....*.....**...
	.............**.........................*.*.....*......*..
	............*.*.....**..................*........*........
	...................*.*............................*.......
	.*...................*.............................*......
	.**.....*...........................................*.....
	*.*.....**...........................................*....
	.......*.*............................................*...
	.......................................................*.*
	........................................................**
	..........................................................
	..........................................................
	..........................................................
	..........................................................
	..........................................................
	..........................................................
	..........................................................
	..........................................................
	..........................................................
	..........................................................
	.................................*........................
	................................***.......................
	...............................**.*.......................
	...............................***........................
	................................**........................
     This reaction uses spaceships on both sides of the line which need
   to be synchronized to each other, for example by passing a glider
   through the gap to trigger the creation of the required spaceships
   and gliders.
     No simple mechanism is known to mend the gap which lies completely
   on one side of the line.  However, it is technically possible to use
   {construction arm} {technology} to push objects through the gap to
   build and trigger a {seed} for the required {synchronized} {signal}s
   on the other side.

:line puffer:  A {puffer} which produces its output by means of an
   orthogonal line of cells at right angles to the direction of travel.
   The archetypal line puffer was found by Alan Hensel in March 1994,
   based on a {spaceship} found earlier that month by Hartmut Holzwart.
   The following month Holzwart found a way to make {extensible} c/2
   line puffers, and Hensel found a much smaller stabilization the
   following day.  But in October 1995 Tim Coe discovered that for large
   widths these were often unstable, although typically lasting millions
   of generations.  In May 1996, however, Coe found a way to fix the
   instability.  The resulting puffers appear to be completely stable
   and to exhibit an exponential increase in period as a function of
   width, although neither of these things has been proved.
     Line puffers have enabled the construction of various difficult
   periods for c/2 spaceships and puffers, including occasionally
   periods which are not multiples of 4 and which would therefore be
   impossible to attain with the usual type of construction based on
   {standard spaceship}s.  (See {frothing puffer} for another method of
   constructing such periods.)  In particular, the first c/2 {rake} with
   period not divisible by 4 was achieved in January 2000 when David
   Bell constructed a p42 {backrake} by means of line puffers.
     See also {hivenudger} and {puff suppressor}.

:line ship:  A {spaceship} in which the front end is a {linestretcher},
   the line being eaten by the back end.

:linestretcher:  A {wickstretcher} that stretches a single diagonal line
   of cells.  The first example was constructed by Jason Summers in
   March 1999; this was c/12 and used {switch engine} based puffers
   found earlier by Dean Hickerson.  The first c/4 example was found by
   Hartmut Holzwart in November 2004.

:loading dock: (p3)  Found by Dave Buckingham, September 1972.
	....*....
	..***....
	.*...**..
	*.**...*.
	.*...**.*
	..**...*.
	....***..
	....*....

:loaf: (p1)
	.**.
	*..*
	.*.*
	..*.

:loafer: (c/7 orthogonally, p7)  A small {c/7 spaceship} discovered by
   Josh Ball on 17 February 2013:
	.**..*.**
	*..*..**.
	.*.*.....
	..*......
	........*
	......***
	.....*...
	......*..
	.......**
     It has a known 8-glider construction recipe, probably not minimal,
   discovered on the following day:
	.................................*
	...............................**.
	................................**
	.........*........................
	.*........*.......................
	..*.....***.......................
	***...............................
	..................................
	..................................
	.....*............................
	......*...........................
	....***...........................
	........................*.*.......
	.........................**.......
	.........................*........
	..................................
	...........................*.*....
	...........................**.....
	............................*.....
	...............................***
	...............................*..
	................................*.
	..................................
	..................................
	..................................
	..................................
	..................................
	..................................
	.....**...........................
	......**..........................
	.....*............................
   The loafer was therefore the first new glider-constructible spaceship
   in almost a decade.  (A {glider synthesis} for a 2c/5 ship,
   {60P5H2V0}, was found in March 2003.)

:loaflipflop: (p15)  Here four {pentadecathlon}s {hassle} a {loaf}.
   Found by Robert Wainwright in 1990.
	................*.................
	...............***................
	..................................
	..................................
	...............***................
	..................................
	...............*.*................
	...............*.*................
	..................................
	...............***................
	..................................
	..................................
	...............***................
	................*.................
	..................................
	.*..*.**.*..*...............**....
	**..*....*..**...**.......*....*..
	.*..*.**.*..*...*..*.....*......*.
	................*.*.....*........*
	.................*......*........*
	........................*........*
	.........................*......*.
	..........................*....*..
	............................**....
	..................***.............
	.................*...*............
	................*.....*...........
	..................................
	...............*.......*..........
	...............*.......*..........
	..................................
	................*.....*...........
	.................*...*............
	..................***.............

:loaf on loaf:  = {bi-loaf}

:loaf pull:  The following glider/loaf collision, which pulls a loaf
   (3,1) toward the glider source:
	.*.....
	*.*....
	*..*...
	.**....
	.......
	.......
	....***
	....*..
	.....*.

:loaf siamese barge: (p1)
	..**.
	.*..*
	*.*.*
	.*.*.
	..*..

:lobster: (c/7 diagonally, p7)  A spaceship discovered by Matthias
   Merzenich in August 2011, the first diagonally travelling
   {c/7 spaceship} to be found. It consists of two {glider}s pulling a
   {tagalong} that then rephases them.
	............***...........
	............*.............
	.............*..**........
	................**........
	............**............
	.............**...........
	............*..*..........
	..........................
	..............*..*........
	..............*...*.......
	...............***.*......
	....................*.....
	**..*.*.............*.....
	*.*.**.............*......
	*....*..**.............**.
	......*...*......**..**..*
	..**......*......*..*.....
	..**....*.*....**.........
	.........*.....*...*...*..
	..........*..*....**......
	...........**...*.....*.*.
	...............*........**
	...............*....*.....
	..............*...*.......
	..............*.....**....
	...............*.....*....

:logarithmic growth:  A pattern whose {population} or {bounding box}
   grows no faster than logarithmically, asymptotic to n.log(t) for some
   constant n.  The first such pattern constructed was the
   {caber tosser} whose population is logarithmic, but whose bounding
   box still grows linearly.  The first pattern whose bounding box and
   population both grow logarithmically was constructed by Jason Summers
   with Gabriel Nivasch in 2003.  For a pattern with a slower growth
   rate than this, see {Osqrtlogt}.

:LoM:  = {lumps of muck}

:lone dot agar:  An {agar} in which every live cell is isolated in every
   generation.  There are many different lone dot agars.  All of them
   are {phoenix}es.  In 1995 Dean Hickerson and Alan W. Hensel found
   stabilizations for finite patches of ten lone dot agars to create
   period 2 oscillators.  One of these is shown below:
	....**..**..**..**..**..**..**..**....
	....*..*.*..*..*.*..*..*.*..*..*.*....
	.....*.......*.......*.......*........
	........*.......*.......*.......*.....
	**..*.*.....*.*.....*.*.....*.*.....**
	*.*.....*.*.....*.*.....*.*.....*.*..*
	....*.......*.......*.......*.......*.
	.*.......*.......*.......*.......*....
	*..*.*.....*.*.....*.*.....*.*.....*.*
	**.....*.*.....*.*.....*.*.....*.*..**
	.....*.......*.......*.......*........
	........*.......*.......*.......*.....
	**..*.*.....*.*.....*.*.....*.*.....**
	*.*.....*.*.....*.*.....*.*.....*.*..*
	....*.......*.......*.......*.......*.
	.*.......*.......*.......*.......*....
	*..*.*.....*.*.....*.*.....*.*.....*.*
	**.....*.*.....*.*.....*.*.....*.*..**
	.....*.......*.......*.......*........
	........*.......*.......*.......*.....
	**..*.*.....*.*.....*.*.....*.*.....**
	*.*.....*.*.....*.*.....*.*.....*.*..*
	....*.......*.......*.......*.......*.
	.*.......*.......*.......*.......*....
	*..*.*.....*.*.....*.*.....*.*.....*.*
	**.....*.*.....*.*.....*.*.....*.*..**
	.....*.......*.......*.......*........
	........*.......*.......*.......*.....
	**..*.*.....*.*.....*.*.....*.*.....**
	*.*.....*.*.....*.*.....*.*.....*.*..*
	....*.......*.......*.......*.......*.
	.*.......*.......*.......*.......*....
	*..*.*.....*.*.....*.*.....*.*.....*.*
	**.....*.*.....*.*.....*.*.....*.*..**
	.....*.......*.......*.......*........
	........*.......*.......*.......*.....
	....*.*..*..*.*..*..*.*..*..*.*..*....
	....**..**..**..**..**..**..**..**....

:lonely bee:  = {worker bee}

:long:  A term applied to an object that is of the same basic form as
   some standard object, but longer.  For examples see {long barge},
   {long boat}, {long bookend}, {long canoe}, {long shillelagh},
   {long ship} and {long snake}.

:long^3:  The next degree of longness after {long long}.  Some people
   prefer "extra long".

:long^4:  The next degree of longness after {long^3}.  Some people
   prefer "extra extra long".

:long barge: (p1)
	.*...
	*.*..
	.*.*.
	..*.*
	...*.

:long boat: (p1)
	.*..
	*.*.
	.*.*
	..**
   A long boat can be used as a 90-degree or 180-degree {one-time}
   {turner}.

:long bookend:  The following {induction coil}, longer than a {bookend}.
	...**
	*...*
	****.

:long canoe: (p1)
	....**
	.....*
	....*.
	...*..
	*.*...
	**....

:long hat:  = {loop}

:long hook:  = {long bookend}

:long house:  = {dock}

:long integral: (p1)
	..**
	.*.*
	.*..
	..*.
	*.*.
	**..

:long long:  The next degree of longness after {long}.  Some people
   prefer "very long".

:long long barge: (p1)
	.*....
	*.*...
	.*.*..
	..*.*.
	...*.*
	....*.

:long long boat: (p1)
	.*...
	*.*..
	.*.*.
	..*.*
	...**

:long long canoe: (p1)
	.....**
	......*
	.....*.
	....*..
	...*...
	*.*....
	**.....

:long long ship: (p1)
	**...
	*.*..
	.*.*.
	..*.*
	...**

:long long snake: (p1)
	**....
	*.*...
	...*.*
	....**

:long shillelagh: (p1)
	**..**
	*..*.*
	.**...

:long ship: (p1)
	**..
	*.*.
	.*.*
	..**

:long sinking ship:  = {long canoe}

:long snake: (p1)
	**...
	*.*.*
	...**

:loop: (p1)
	.**..
	*..*.
	.*.*.
	**.**

:looping spaceship:  = {reflectorless rotating oscillator}

:lossless elbow:  A stationary {elbow} in a {construction arm} {toolkit}
   that allows a {recipe} to turn a corner with no exponential increase
   in construction cost.  Compare {slow elbow}.  It is theoretically
   possible to construct lossless elbows for early construction arms
   such as the one in the {10hd Demonoid}, but these would currently
   have to be very large.
     The lossless elbow that has been used the most in practice is the
   {Snark}, which can be constructed directly on a {single-channel}
   {construction lane} using a {Snarkmaker} {recipe}.  Controlled
   demolition of a Snark is also possible, to remove a temporary elbow
   that is no longer needed, and leave a {hand} target in its place if
   necessary for further construction.
     A {Silver reflector} was used as a lossless elbow in the first
   {spiral growth} pattern, attached to a separate
   {universal constructor} component.

:low-density Life:  = {sparse Life}

:lumps of muck:  The common evolutionary sequence that ends in the
   {blockade}.  The name is sometimes used of the blockade itself, and
   can in general be used of any stage of the evolution of the
   {stairstep hexomino}.

:LW emulator: (p4)  The smallest (and least useful) {emulator}, found by
   Robert Wainwright in June 1980.
	..**.*..*.**..
	..*........*..
	...**....**...
	***..****..***
	*..*......*..*
	.**........**.

:LWSS: (c/2 orthogonally, p4)  A lightweight spaceship, the smallest
   known orthogonally moving {spaceship}, and the second most common
   (after the {glider}).  Found by Conway when one formed from a random
   soup in 1970.  See also {MWSS} and {HWSS}.
	.*..*
	*....
	*...*
	****.
     The LWSS possesses a {tail spark} which can easily {perturb} other
   objects which grow into its path.  The spaceship can also perturb
   some objects in additional ways.  For examples, see {blinker ship},
   {hivenudger}, and {puffer train}.
     Dave Buckingham found that the LWSS can be synthesized in several
   different ways using three gliders, and can be constructed from two
   gliders and another small object in several more ways.  Here is the
   fastest {synthesis}:
	.*.....
	*......
	***....
	.....**
	....**.
	......*
	.......
	..**...
	...**..
	..*....

:LWSS emulator:  = {LW emulator}

:LWSS-glider bounce:  The following reaction in which a {LWSS} and a
   {glider} collide to form a glider heading back between the two input
   paths:
	.****........
	*...*........
	....*.....***
	*..*......*..
	...........*.
   This is one way to {inject} a glider into a existing glider stream.
   The {infinite glider hotel} uses this reaction.

:LWSS-LWSS bounce:  The following {symmetric} reaction in which two
   {LWSS}s collide head-on to form two {glider}s heading apart at 90
   degrees from each other.  Compare {LWSS-LWSS deflection}.
	*..*.......*..*
	....*.....*....
	*...*.....*...*
	.****.....****.
   This provides one way to {inject} a {glider} into a existing glider
   stream.  Another use is described in {metamorphosis}.

:LWSS-LWSS deflection:  The following symmetric reaction in which two
   LWSSs collide nearly head-on to form two gliders heading apart at 180
   degrees from each other.  Compare {LWSS-LWSS bounce}.
	.........*..*
	........*....
	........*...*
	........****.
	.............
	.****........
	*...*........
	....*........
	*..*.........

:LWSS-to-G:  See {135-degree MWSS-to-G}.

:LWTDS:  Life Worker Time Deficiency Syndrome.  Term coined by Dieter
   Leithner to describe the problem of having to divide scarce time
   between Life and real life.

:LW volcano:  = {toaster}

:Lx200:  A {composite conduit}, one of the original sixteen
   {Herschel conduit}s, discovered by Paul Callahan in June 1997.  It is
   made up of two {elementary conduit}s, HL141B + {BFx59H}. The Lx200
   and {F166} conduits are the two original {dependent conduit}s
   (several more have since been discovered.)  After 200 ticks, it
   produces an inverted {Herschel} turned 90 degrees counterclockwise at
   (17, -40) relative to the input.  Its {recovery time} is 90 ticks.
   It can be made {Spartan} by replacing the {snake}s with {eater1}s in
   one of two orientations. A {ghost Herschel} in the pattern below
   marks the output location:
	.....................**.............
	......................*.............
	......................***...........
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	.......................**...........
	.......................**...........
	....................................
	..............................*.**..
	..............................**.*..
	....................................
	....................................
	..............*.**..................
	..............**.*..................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	................................**..
	................................*.*.
	.**...............................*.
	***.**............................**
	.**.***.**..........................
	***.**..**..........................
	**..................................
	....................................
	....................................
	....................................
	................................**..
	................................**..
	....................................
	......**............................
	.......*............................
	....***.........................**..
	....*...........................**..
	..................**................
	.................*.*................
	.................*..................
	................**........**........
	..........................*.........
	...........................***......
	.............................*......
   The input shown here is a {Herschel great-grandparent}, since the
   input reaction is catalysed by the {transparent} block before the
   Herschel's standard form can appear.

:macrocell:  A format used by {Golly} and its {hashlife} algorithm,
   capable of storing repetitive patterns very efficiently, even if they
   contain a large number of cells.  For example, a filled square 2^167
   cells on a side can be stored in less than three kilobytes in
   macrocell format, or about 800 bytes in compressed macrocell format.
   The square's total population is over a googol, 10^100; the number of
   atoms in the observable universe is only about 10^80.
     This high level of compression is obtained by defining a tree
   structure composed of increasingly large cell "tiles" with
   power-of-two dimensions.  Tile definitions of any size are re-used
   whenever they appear multiple times in a large pattern (at the same
   power-of-two offset).  For example, the following is a macrocell
   encoding of a complex {pseudo still life} arrangement of {ship}s,
   with a total population over 2500 cells:
	[M2] (golly 3.0)
	#R B3/S23
	.**.**$*.*.*.*$**...**$$**...**$*.*.*.*$.**.**$
	4 0 1 1 1
	5 2 0 2 2
	6 3 3 0 3
	7 4 4 4 4
     The first line after the #R rule line defines a quadtree tile at
   the lowest level - a level-3 tile in this case, meaning a 2^3 square
   area.  At this level the pattern is encoded in a modified ASCII
   format with dollar signs as line separators.  The next line, #2,
   defines a level-4 quadtree tile, made from one empty level-3 tile in
   the northwest corner (0), and three copies of the level-3 tile that
   was defined on the previous line (1).  Lines 3, 4, and 5 similarly
   define level 5, 6, and 7 quadtree tiles by giving the line numbers of
   four tiles of the next lower size.
     Many patterns are only moderately repetitive, so macrocell format
   is somewhat less successful at compressing them.  Certainly most
   patterns are not nearly as regular as the artificial example above:
   there are usually many different tiles defined at each level, not
   just one.  Chaotic patterns, such as {ash} from random {soup}s,
   usually need so many different tile definitions that they can be
   stored more efficiently using {rle} format.

:macro-spaceship:  A {self-constructing} or {self-supporting}
   {spaceship}, such as the {Caterpillar}, {Centipede},
   {half-baked knightship}, {waterbear}, {Demonoid}, {Orthogonoid}, and
   {Caterloopillar}.  Engineered spaceships of these types tend to be
   much larger and more complex than {elementary} spaceships.

:mango: (p1)  A relatively rare 180-degree rotationally {symmetric}
   8-{bit} {still life}. The {acorn} produces a mango as part of its
   {ash}.
	.**..
	*..*.
	.*..*
	..**.

:mathematician: (p5)  Found by Dave Buckingham, 1972.
	....*....
	...*.*...
	...*.*...
	..**.**..
	*.......*
	***...***
	.........
	*********
	*.......*
	...****..
	...*..**.

:Max:  A name for the smallest known {spacefiller}.  The name represents
   the fact that the growth rate is the fastest possible.  (This has not
   quite been proved, however.  There remains the possibility, albeit
   not very likely, that a periodic {agar} could have an average
   {density} greater than 1/2, and a spacefiller stretching such an agar
   at the same speed as the known spacefillers would have a faster
   average growth rate.)

:mazing: (p4)  In terms of its minimum {population} of 12 this ties with
   {mold} as the smallest p4 {oscillator}.  Found by Dave Buckingham in
   December 1973.  For some constructions using mazings, see {popover}
   and {sixty-nine}.
	...**..
	.*.*...
	*.....*
	.*...**
	.......
	...*.*.
	....*..

:mc:  = {macrocell}

:medium fish:  = {MWSS}

:megacell:  = {p1 megacell}.

:memory cell:  A type of information storage {circuit} useful in many
   patterns that perform complex logical operations.  Most commonly a
   memory cell can store a single bit of information.  See for example
   {demultiplexer}, {honey bit}, and {boat-bit}.  Depending on the
   application, the circuit may be a {toggle circuit} or a
   {permanent switch}, or it may be possible to send one or more signals
   to set the circuit to a "1" state, as can be done with a {keeper}
   mechanism.  In that case a different input signal must be used to
   test the current state, usually with a {destructive read} reaction.
     A more complicated example can be found in the {Osqrtlogt} pattern,
   which destructively reads a growing 2-dimensional array of minimal
   memory cells.  Each memory cell may either contain a {boat} (below
   left) or empty space (below right), with no permanent circuitry
   anywhere near:
	...............**........................**
	...............**........................**
	...........................................
	...........*...............................
	..........*.*..............................
	...........**..............................
	...........................................
	...........................................
	......**........................**.........
	.....*..*......................*..*........
	......**........................**.........
	...........................................
	...........................................
	.**........................**..............
	*..*......................*..*.............
	.**......***...............**......***.....
	.........*.........................*.......
	..........*.........................*......
   The two {beehive}s and the {block} are placed by {slow salvo}s, after
   an initial 90-degree {2-glider collision} that produces a target
   {honey farm}.  The beehive {constellation} acts as a {one-time}
   {turner} for an incoming {glider}.  If the boat is present, it acts
   as a second one-time turner for that glider, sending back a "1"
   signal.  The "backstop" {block} in the northeast is destroyed cleanly
   in either the "0" or the "1" case.

:Merzenich's p11: (p11)  Found by Matthias Merzenich in December 2010.
	...........**........
	............*........
	............*.*......
	..........**.*.*.....
	.........*.*.*.*.....
	........*.*..*..**...
	.......*.....*....*..
	......*.......****...
	.....*............***
	....*.....*.....**..*
	...*.*...*.*...*.*...
	*..**.....*.....*....
	***............*.....
	...****.......*......
	..*....*.....*.......
	...**..*..*.*........
	.....*.*.*.*.........
	.....*.*.**..........
	......*.*............
	........*............
	........**...........

:Merzenich's p18: (p18)  Found by Matthias Merzenich in June 2011.
	...**............
	....*............
	..*.*.**.........
	.*.*.*.*...**....
	.*.*........*....
	**.*........*.**.
	...*.**....**.*..
	...*..........*..
	**.*.*.....***.**
	*..*.*.*..*..*.*.
	..*..*.****.*..*.
	...**.*....**.*..
	......*..*...*...
	......*.*.***....
	.......**.*......

:metacatacryst:  A 52-cell pattern exhibiting quadratic growth.  Found
   by Nick Gotts, December 2000.  This was for some time the smallest
   known pattern (in terms of initial population) with superlinear
   growth.  See {switch-engine ping-pong} for the lowest-population
   {superlinear growth} pattern as of July 2018, along with a list of
   the record-holders.

:metacell:  CA logic circuitry that emulates the behavior of a single
   cell. The circuitry is hard-wired to emulate a particular CA rule,
   but changing the rule is usually a matter of making simple
   adjustments. Known examples include David Bell's original 500x500
   {unit Life cell}, Jared Prince's {Deep Cell}, Brice Due's
   {OTCA metapixel}, and Adam P. Goucher's {megacell}.

:metamorphosis:  An {oscillator} built by Robert Wainwright that uses
   the following reaction (found by Bill Gosper) to turn {glider}s into
   {LWSS}, and converts these LWSS back into gliders by colliding them
   head on using an {LWSS-LWSS bounce}.  There are two ways to do the
   following reaction, because the {twin bees shuttle spark} is
   {symmetric}.
	...................*.........
	....................*........
	..................***........
	.............................
	.............................
	.............................
	.............................
	.............................
	............*...*.....*.**...
	**.........*.....*....*.*.*..
	**.........*.........*....*..
	...........**...*.....*.*.*..
	.............***......*.**...
	.............................
	.............***.............
	...........**...*............
	**.........*...............**
	**.........*.....*.........**
	............*...*............

:metamorphosis II:  An oscillator built by Robert Wainwright in December
   1994 based on the following p30 {glider}-to-{LWSS} {converter} using
   a {queen bee shuttle pair}.  This converter was first found by Paul
   Rendell, January 1986 or earlier, but wasn't widely known about until
   Paul Callahan rediscovered it in December 1994.
	......................*.
	.....................*..
	.....................***
	........................
	........................
	.........*.*............
	.........*..*...........
	**..........**..........
	**........*...**........
	.....**.....**..........
	....*....*..*...........
	.........*.*............
	........................
	........................
	........................
	........................
	................*.......
	...............***......
	..............*****.....
	.............*.*.*.*....
	.............**...**....
	........................
	........................
	................*.......
	...............*.*......
	...............*.*......
	................*.......
	...............**.......
	...............**.......
	...............**.......

:metapixel:  See {metacell}, {OTCA metapixel}.

:methuselah:  Any small pattern that stabilizes only after a long time.
   Term coined by Conway.  Examples include {rabbits}, {acorn}, the
   {R-pentomino}, {blom}, {Iwona}, {Justyna} and {Lidka}.  See also
   {ark}.

:Mickey Mouse: (p1)  The following {still life}, named by Mark Niemiec:
	.**....**.
	*..*..*..*
	*..****..*
	.**....**.
	...****...
	...*..*...
	....**....

:middleweight emulator:  = {MW emulator}

:middleweight spaceship:  = {MWSS}

:middleweight volcano:  = {MW volcano}

:mini pressure cooker: (p3)  Found by Robert Wainwright before June
   1972.  Compare {pressure cooker}.
	.....*.....
	....*.*....
	....*.*....
	...**.**...
	*.*.....*.*
	**.*.*.*.**
	...*...*...
	...*.*.*...
	....*.*....
	.....*.....

:M.I.P. value:  The maximum {population} divided by the initial
   population for an unstable pattern.  For example, the {R-pentomino}
   has an M.I.P. value of 63.8, since its maximum population is 319.
   The term is no longer in use.

:MIT oscillator:  = {cuphook}

:MMM breeder:  See {breeder}.

:MMS breeder:  See {breeder}.

:mod:  The smallest number of generations it takes for an {oscillator}
   or {spaceship} to reappear in its original form, possibly subject to
   some rotation or reflection.  The mod may be equal to the {period},
   but it may also be a quarter of the period (for oscillators that
   rotate 90 degrees every quarter period) or half the period (for other
   oscillators which rotate 180 degrees every half period, and also for
   {flipper}s).

:mold: (p4)  Found by Achim Flammenkamp in 1988, but not widely known
   until Dean Hickerson rediscovered it (and named it) in August 1989.
   Compare with {jam}.  In terms of its minimum {population} of 12 it
   ties with {mazing} as the smallest p4 {oscillator}.  But in terms of
   its 6x6 {bounding box} it wins outright.  In fact, of all oscillators
   that fit in a 6x7 box it is the only one with {period} greater than
   2.
	...**.
	..*..*
	*..*.*
	....*.
	*.**..
	.*....

:monochromatic salvo:  A {slow salvo} that uses gliders of only one
   colour.  For example, the slow salvos generated by
   {half-baked knightship}s are monochromatic, because they are
   generated by a single type of reaction which can happen at any
   position along a diagonal line.  The smallest possible step size is
   one {full diagonal} (1fd), which is two {half diagonal}s (2hd), which
   means that any single glider-producing reaction can only reach half
   of the available glider {lane}s.  See {colour of a glider}.

:monogram: (p4)  Found by Dean Hickerson, August 1989.
	**...**
	.*.*.*.
	.**.**.
	.*.*.*.
	**...**

:monoparity salvo:  A {slow salvo} that uses gliders of only one
   {parity}.  Compare {monochromatic salvo}.

:Moore neighbourhood:  The set of all cells that are orthogonally or
   diagonally adjacent to a cell or group of cells.  The Moore
   neighbourhood of a cell can be thought of as the points at a
   Chebyshev distance of 1 from that cell.  Compare
   {von Neumann neighbourhood}.  The Conway's Life rule is based on the
   Moore neighborhood, as are all the "Life-like" rules and many other
   commonly investigated rule families.
     Cell neighbourhoods can also be defined with a higher range. The
   Moore neighbourhood of range n can be defined recursively as the
   Moore neighbourhood of the Moore neighbourhood of range n-1.  For
   example, the Moore neighbourhood of range 2 includes all cells that
   are orthogonally or diagonally adjacent to the standard Moore
   neighbourhood.

:moose antlers: (p1)
	**.....**
	*.......*
	.***.***.
	...*.*...
	....*....

:mosquito:  See {mosquito1}, {mosquito2}. {mosquito3}, {mosquito4} and
   {mosquito5}.

:mosquito1:  A {breeder} constructed by Nick Gotts in September 1998.
   The original version had an initial population of 103, which was then
   the smallest for any known pattern with superlinear growth (beating
   the record previously held by {Jaws}).  This was reduced to 97 by
   Stephen Silver the following month, but was then almost immediately
   superseded by {mosquito2}.
     Mosquito1 consists of the classic {puffer train} plus four {LWSS}
   and four {MWSS} (mostly in {predecessor} form, to keep the population
   down).  Once it gets going it produces a new block-laying
   {switch engine} (plus a lot of junk) every 280 generations.  It is
   therefore an MMS breeder, albeit a messy one.

:mosquito2:  A {breeder} constructed by Nick Gotts in October 1998. Its
   initial population of 85 was for a couple of hours the smallest for
   any known pattern with superlinear growth, but was then beaten by
   {mosquito3}.
     Mosquito2 is very like {mosquito1}, but uses two fewer {MWSS} and
   one more {LWSS}.

:mosquito3:  A {breeder} constructed by Nick Gotts in October 1998. Its
   initial population of 75 was at the time the smallest for any known
   pattern with superlinear growth, but was beaten a few days later by
   {mosquito4}.
     Mosquito3 has one less {LWSS} than {mosquito2}.  It is somewhat
   different from the earlier mosquitoes in that the {switch engine}s it
   makes are glider-producing rather than block-laying.

:mosquito4:  A slightly improved version of {mosquito3} which Stephen
   Silver produced in October 1998 making use of another discovery of
   Nick Gotts (September 1997): an 8-cell pattern that evolves into a
   {LWSS} plus some junk.  Mosquito4 is a {breeder} with an initial
   population of 73, at the time the smallest for any known pattern with
   superlinear growth, but superseded a few days later by {mosquito5}.

:mosquito5:  A slightly improved version of {mosquito4} which Nick Gotts
   produced in October 1998.  The improvement is of a similar nature to
   the improvement of mosquito4 over mosquito3.  Mosquito5 is a
   {breeder} with an initial population of 71.  This was the smallest
   population for any known pattern with superlinear growth until it was
   superseded by {teeth}.  See {switch-engine ping-pong} for the
   smallest such pattern as of July 2018, along with a list of the
   record-holders.

:mould:  = {mold}

:moving sawtooth:  A {sawtooth} such that no cell is ON for more than a
   finite number generations.  David Bell constructed the first pattern
   of this type, with a c/2 front end and a c/3 back end.  The front end
   is a {blinker puffer}.  The back end ignites the {blinker fuse}.
     The smallest currently known moving sawtooth was constructed in
   April 2011 by a conwaylife.com forum user with the handle
   'cloudy197'.  The c/2 front end is a {bi-block puffer}.  The 2c/5
   back end ignites the {bi-block fuse}.

:MSM breeder:  See {breeder}.

:multiple roteightors: (p8)  An {extensible} oscillator family
   consisting of one or more {roteightor} rotors, discovered by Dean
   Hickerson in 1990.
	....................*...........
	........**........***...........
	.........*.......*..............
	.........*.*.....**.............
	..........**.............*......
	.......................***......
	....**........***.....*.........
	.....*.......*..*......*........
	.....*.*........*..*...*......*.
	......**..*....*..*.........***.
	.........*........*..*.....*....
	**.......*..*.....***......**...
	.*.......***....................
	.*.*............................
	..**....................***.....
	...............***.....*..*.....
	......***.....*..*........*.....
	.....*..*........*..*....*..**..
	........*..*....*..*........*.*.
	...*...*..*........*..*.......*.
	...*......*..*.....***........**
	....*.....***...................
	.***....................**......
	.*......................*.*.....
	........**......***.......*.....
	.........*.....*..*.......**....
	......***.........*.............
	......*......*...*..**..........
	.............*......*.*.........
	..............*.......*.........
	...........***........**........
	...........*....................

:multiplicity:  In a {reflectorless rotating oscillator}, the maximum
   number n of independent patterns that can orbit a single point, in a
   way that reduces the period of the combined oscillator by a factor of
   n.

:multi-state Life:  = {colourised Life}

:multum in parvo: (stabilizes at time 3933)  A {methuselah} found by
   Charles Corderman, but not as long-lasting as his {acorn}.
	...***
	..*..*
	.*....
	*.....

:muttering moat:  Any {oscillator} whose {rotor} consists of a closed
   chain of cells each of which is adjacent to exactly two other rotor
   cells.  Compare {babbling brook}.  Examples include the {bipole}, the
   {blinker}, the {clock}, the {cuphook}, the {Gray counter}, the
   {quad}, the {scrubber}, the {skewed quad} and the p2 {snake pit}. The
   following diagram shows a p2 example (by Dean Hickerson, May 1993)
   with a larger rotor.  See {ring of fire} for a very large one.
	**.....
	*.*.**.
	.....*.
	.*..*..
	..*....
	..*.*.*
	.....**

:MW emulator: (p4)  Found by Robert Wainwright in June 1980.  See also
   {emulator} and {filter}.
	.......*.......
	..**.*...*.**..
	..*.........*..
	...**.....**...
	***..*****..***
	*..*.......*..*
	.**.........**.

:MWSS: (c/2 orthogonally, p4)  A middleweight spaceship, the third most
   common {spaceship}.  Found by Conway in 1970 by modifying a {LWSS}.
   See also {HWSS}.
	...*..
	.*...*
	*.....
	*....*
	*****.
     The MWSS possesses both a {tail spark} and a {belly spark} which
   can easily perturb other objects as it passes by.  The spaceship can
   also perturb some objects in additional ways.  For examples see
   {blinker puffer} and {glider turner}.
     Dave Buckingham found that the MWSS can be synthesized using three
   gliders, and can be constructed from two gliders and another small
   object in several more ways.  Here is the {glider synthesis}:
	...........*..
	...........*.*
	...........**.
	..............
	..............
	.*......**....
	.**.....*.*...
	*.*.....*.....

:MWSS emulator:  = {MW emulator}

:MWSS out of the blue:  The following reaction, found by Peter Rott in
   November 1997, in which a {LWSS} passing by a p46 {oscillator}
   creates a {MWSS} travelling in the opposite direction.  Together with
   some reactions found by Dieter Leithner, and an LWSS-turning reaction
   which Rott had found in November 1993 (but which was not widely known
   until Paul Callahan rediscovered it in June 1994) this can be used to
   prove that there exist {gliderless} guns for LWSS, MWSS and {HWSS}
   for every period that is a multiple of 46.
	*..*.................................
	....*................................
	*...*................................
	.****................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	...................**..............**
	..................**...............**
	...................*****.............
	..**................****.............
	..**.....*...........................
	........***.........****.............
	.......*.*.*.......*****.............
	........*..*......**...............**
	........***........**..............**
	.........*...........................
	.....................................
	.....................................
	.....................................
	.....................................
	..*.......*..........................
	.....................................
	***.......***........................
	.**.**.**.**.........................
	..***...***..........................
	...*.....*...........................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	..**.....**..........................
	..**.....**..........................

:MWSS-to-G:  See {135-degree MWSS-to-G}, {45-degree MWSS-to-G}.

:MW volcano: (p5)  Found by Dean Hickerson in April 1992.
	......*......
	....*...*....
	.............
	...*.....*...
	.***.***.***.
	*...**.**...*
	*.***.*.****.
	.*...........
	...*.*.*.**.*
	..**.***.*.**
	...*.*..*....
	...*..**.....
	..**.........

:My Experience with B-heptominos in Oscillators:  An article by Dave
   Buckingham (October 1996) available from
   {http://conwaylife.com/ref/lifepage/patterns/bhept/bhept.html}.  It
   describes his discovery of {Herschel conduit}s, including sufficient
   (indeed ample) {stable} conduits to enable, for the first time, the
   construction of period n oscillators and {true} period n guns for
   every sufficiently large integer n.  See {Herschel loop} and {emu}.

:natural:  Occurring often in random patterns.  There is no precise
   measure of naturalness, since the most useful definition of "random"
   in this context is open to debate.  Nonetheless, it is clear that
   objects such as {block}s, {blinker}s, {beehive}s and {glider}s are
   very natural, while {eater2}s, {dart}s, {gun}s, etc., are not.

:natural Heisenburp: (p46)  A {twin bees shuttle pair} arrangement found
   by Brice Due in 2006.  A {glider} passes through the reaction area of
   the shuttle pair completely unaffected.  However, a
   {Heisenburp effect} causes a second glider to be created "out of the
   blue", following behind the first at a 2{hd} offset.
	..................**.................
	.................*.*...............**
	.................*.................**
	.................***.................
	.....................................
	.....................................
	.....................................
	.................***.................
	........**.......*.................**
	........**.......*.*...............**
	..................**.................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.*.....*.............................
	***...***............................
	*.**.**.*............................
	..**.**..........**..................
	..**.**..........*.*.................
	..**.**..........*...................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	**.....**............................
	**.....**............................

:ND read:  = {non-destructive read}

:negative spaceship:  A type of {signal} travelling through a periodic
   {agar} such as {zebra stripes}. The leading edge of the signal
   removes the agar, and the trailing edge rebuilds the agar some time
   later.  The distance between the two edges is sometimes adjustable,
   as shown in {lightspeed bubble}.  The central part of the "spaceship"
   may consist of dying sparks or even simple empty space.
     Below is a sample period-5 negative spaceship, found by Hartmut
   Holzwart in March 2007, in a small stabilized section of
   {zebra stripes} agar:
	.*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*.
	.*******************************************************.
	.........................................................
	.*****************************..***..*******************.
	*..............................**...**..................*
	.************************..***...**...****..************.
	..........................**...............**............
	.************************..***...**.....**...**..*******.
	*..............................**...*.**........**......*
	.************************..***..***...**.....**...******.
	..........................**............**.**............
	.************************...*****..........**.....******.
	*............................*...............**.**......*
	.************************.....*.........*.......**..****.
	..........................*.*......*...*..........**.....
	.************************...*.*.*****......*.......*****.
	*..............................***...*......*...........*
	.************************...*.*.*****......*.......*****.
	..........................*.*......*...*..........**.....
	.************************.....*.........*.......**..****.
	*............................*...............**.**......*
	.************************...*****..........**.....******.
	..........................**............**.**............
	.************************..***..***...**.....**...******.
	*..............................**...*.**........**......*
	.************************..***...**.....**...**..*******.
	..........................**...............**............
	.************************..***...**...****..************.
	*..............................**...**..................*
	.*****************************..***..*******************.
	.........................................................
	.*******************************************************.
	.*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*.
   The "spaceship" travels to the left at the {speed of light}, so it
   will eventually reach the edge of any finite patch and destroy itself
   and its supporting agar.

:negentropy: (p2)  Compare {Hertz oscillator}.
	...**.*....
	...*.**....
	...........
	....***....
	...*.*.*.**
	...**..*.**
	**.*...*...
	**.*...*...
	....***....
	...........
	....**.*...
	....*.**...

:neighbour:  Any of the eight cells adjacent to a given cell.  A cell is
   therefore not considered to be a neighbour of itself, although the
   neighbourhood used in Life does in fact include this cell (see
   {cellular automaton}).

:new five: (p3)  Found by Dean Hickerson, January 1990.
	..**.....
	.*..*....
	.*.*..*..
	**.*.**..
	*........
	.***.****
	.....*..*
	*.**.....
	**.**....

:new gun: (p46)  An old name for the period 46 glider gun show below.
   This was found by Bill Gosper in 1971, and was the second basic
   glider gun found (after the {Gosper glider gun}).  It produces a
   period 46 glider {stream}.
	.........................**.....**
	.........................**.....**
	..................................
	..................................
	..................................
	..................................
	..................................
	..................................
	..................................
	..................................
	..................................
	..................................
	..................................
	...........................**.**..
	..........................*.....*.
	..................................
	.........................*.......*
	.........................*..*.*..*
	.........................***...***
	..................................
	..................................
	..................................
	..................................
	.................*................
	**...............**...............
	**................**..............
	.............**..**...............
	..................................
	..................................
	..................................
	.............**..**...............
	**................**.......**.....
	**...............**........**.....
	.................*................
     A number of other ways of constructing a gun from two
   {twin bees shuttle}s have since been found.  See {edge shooter} for
   one of these, and see also {p46 gun}.

:Noah's ark:  The following diagonal {puffer} consisting of two
   {switch engine}s.  This was found by Charles Corderman in 1971. The
   name comes from the variety of objects it leaves behind: blocks,
   blinkers, beehives, loaves, gliders, ships, boats, long boats,
   beacons and block on tables.
	..........*.*..
	.........*.....
	..........*..*.
	............***
	...............
	...............
	...............
	...............
	...............
	.*.............
	*.*............
	...............
	*..*...........
	..**...........
	...*...........
     See also {ark}.

:n-omino:  Any {polyomino} with exactly n cells.

:non-destructive read:  A type of test reaction in {memory cell}
   circuitry, where the information in the memory cell is unchanged and
   can be read again to produce the same result.  One simple type of
   non-destructive read reaction is a {signal} sent to a
   {permanent switch}.  Memory cells with {destructive read} reactions
   are generally simpler and more commonly used.

:nonfiller:  = {space nonfiller}

:non-monotonic:  A {spaceship} is said to be non-monotonic if its
   leading edge falls back in some generations.  The first example
   (shown below) was found by Hartmut Holzwart in August 1992.  This is
   p4 and travels at c/4.  In April 1994, Holzwart found examples of p3
   spaceships with this property, and this is clearly the smallest
   possible period.  Another non-monotonic spaceship is the {weekender}.
	..........**.*.......
	......***.*.***......
	..*.*..........*...**
	**....**.....*...****
	..*.**..*....***.*...
	........*....*.......
	..*.**..*....***.*...
	**....**.....*...****
	..*.*..........*...**
	......***.*.***......
	..........**.*.......

:nonomino switch engine predecessor:  This is the unique nonomino (a
   {polyomino} having 9 cells) whose {evolution} results in a
   {switch engine}, and the smallest polyomino to do so.
	***...
	..*.*.
	..****
     Charles Corderman may have found this object in 1971 while
   exhaustively investigating the {fate} of all the small {polyomino}es.
   Records indicate that he found the {switch engine} while
   investigating the decominoes (polyominoes having 10 cells). However,
   there do not appear to be decominoes which result in a {clean}
   {switch engine}.  If Corderman was examining polyominoes in order of
   size, then this smaller {predecessor} should have been found first in
   any case.

:non-spark:  Something that looks like a spark, but isn't.  An {OWSS}
   produces one of these instead of a {belly spark}, and is destroyed by
   it.

:non-standard spaceship:  Any {spaceship} other than a {glider}, {LWSS},
   {MWSS} or {HWSS}.

:non-trivial:  A non-trivial period-N {oscillator} contains at least one
   cell that oscillates at the full period.  In other words, it is not
   made up solely of separate oscillators with smaller periods. Usually
   it includes a {spark} or other reaction that would not occur if all
   lower-period subpatterns were separated from each other, but some
   exceptions are given under {trivial}.  See also {omniperiodic}.

:novelty generator:  A pattern that appears to have an {unknown fate}
   due to complex feedback loops, for example involving {wave}s of
   gliders shuttling between perpendicular {rake}s.  Novelty generator
   patterns fall short of counting as {chaotic growth}, since the rakes
   continue to be predictable, and much of their {ash} generally remains
   stable.
     It has not been proven conclusively that any particular pattern is
   in fact an infinite novelty generator, since it is always possible
   that periodicity will spontaneously arise if the simulation is
   continued far enough.  In fact this happens quite regularly.  But
   conversely, it has not been proven that periodicity must
   spontaneously arise for all such patterns.  Bill Gosper, Nick Gotts
   and others have done extensive experiments along these lines using
   {Golly}.

:NW31:  One of the most common stable {edge shooter}s.  This
   {Herschel-to-glider} {converter} suppresses the junk ordinarily left
   behind by an evolving {Herschel} while allowing both the
   {first natural glider} and {second natural glider} to escape on
   {transparent lane}s:
	**.......................
	.*.......................
	.*.*.....................
	..**.....................
	.........................
	.........................
	.........................
	.......................**
	.......................**
	.........................
	..*......................
	..*.*....................
	..***....................
	....*....................
	.........................
	.........................
	.........................
	.........................
	.........................
	.........................
	.........................
	...........**............
	............*............
	.........***.............
	.........*...............
   The edge shooter output at the top has no additional {clearance}, so
   its use in creating {convoy}s is limited:  it can only add gliders on
   the outermost lanes of an existing glider {salvo}.  Like the beehive
   version of {SW-2}, either output can be used to build logical OR
   gates, where multiple input {signal} paths are merged onto the same
   output path.
     The complete name for this converter is "NW31T120", where 31 is the
   output glider lane number.  In the above orientation, lane numbers
   get bigger toward the upper right and smaller toward the lower left
   (and may easily be negative).
     The T120 timing measurement means that a canonical NW glider placed
   on lane 31 at time T=120, at (+31, +0) relative to the input
   Herschel, would in theory reach the exact same spacetime locations as
   the converter's output glider does.
     Most converters are not edge shooters and their output lanes are
   not transparent, so they usually have catalysts that would interfere
   with this theoretically equivalent glider.  This is the case for the
   optional third glider output created by the lower {eater1} catalyst:
   the upper eater1 overlaps its {lane}.  For the alternate {block}
   catalyst suppressing this glider output, see {transparent lane}.

:NW31T120:  = {NW31}

:oblique:  Neither diagonal nor orthogonal.  See also {knightship}.

:obo spark:  A {spark} of the form O.O (so called after its {rle}
   encoding).

:octagon II: (p5)  The first known p5 {oscillator}, discovered in 1971
   independently by Sol Goodman and Arthur Taber.  The name is due to
   the latter.
	...**...
	..*..*..
	.*....*.
	*......*
	*......*
	.*....*.
	..*..*..
	...**...

:octagon IV: (p4)  Found by Robert Wainwright, January 1979.
	.......**.......
	.......**.......
	................
	......****......
	.....*....*.....
	....*......*....
	...*........*...
	**.*........*.**
	**.*........*.**
	...*........*...
	....*......*....
	.....*....*.....
	......****......
	................
	.......**.......
	.......**.......

:octomino:  Any 8-cell {polyomino}.  There are 369 such objects.  The
   word is particularly applied to the following octomino (or its
   two-generation successor), which is fairly common but lacks a proper
   name:
	..**
	..**
	***.
	.*..

:odd keys: (p3)  Found by Dean Hickerson, August 1989.  See also
   {short keys} and {bent keys}.
	..........*.
	.*.......*.*
	*.***..**.*.
	.*..*..*....
	....*..*....

:omino:  = {polyomino}

:omniperiodic:  A {cellular automaton} is said to be omniperiodic if it
   has {oscillator}s of all {period}s. It is not known if Life is
   omniperiodic, although this seems likely.  Dave Buckingham's work on
   Herschel conduits in 1996 (see
   {My Experience with B-heptominos in Oscillators}) left only a short
   list of unresolved cases, all with periods of 58 or below.  The list
   has been progressively reduced since then.  Most recently, period 43
   and 53 oscillators were made possible in 2013 by Mike Playle's
   {Snark}.  As of June 2018, no oscillators are known for periods 19,
   23, 38, or 41.  If we insist that the oscillator must be
   {non-trivial}, then 34 should be added to this list.
     Note that if we were to allow infinite oscillators, then all
   periods are certainly possible, as any period of 14 or more can be
   obtained using a {glider} (or {LWSS}) stream, or an infinitely long
   {2c/3} wire containing signals with the desired separation.

:one per generation:  See {grow-by-one object}.

:one-sided spaceship synthesis:  A {glider synthesis} of a {spaceship}
   in which all gliders come from the same side of the spaceship's path.
   Such syntheses are used extensively in the 17c/45 {Caterpillar}.  For
   example, here is a one-sided way to create an {LWSS}.
	...*.....
	....**...
	...**....
	.........
	.........
	.....*...
	...*.*...
	....**...
	.........
	.........
	.........
	.........
	......***
	........*
	.......*.
	.........
	.........
	.........
	***......
	..*......
	.*.......

:one-time:  A term used for {turner}s and {splitter}s, specifying that
   the reaction in question is not repeatable as it would be in a
   {reflector} or {fanout} device.  Instead, the {constellation} is used
   up, usually in a {clean} reaction, but the much more common {dirty}
   turners and splitters are also very useful in some situations.

:onion rings:  For each integer n>1 onion rings of order n is a {stable}
   {agar} of {density} 1/2 obtained by tiling the plane with a certain
   4n x 4n pattern.  The tile for order 3 onion rings is shown below.
   The reader should be able to deduce the form of tiles of other
   orders.
	......******
	.****.*....*
	.*..*.*.**.*
	.*..*.*.**.*
	.****.*....*
	......******
	******......
	*....*.****.
	*.**.*.*..*.
	*.**.*.*..*.
	*....*.****.
	******......

:Online Life-Like CA Soup Search:  =
   {The Online Life-Like CA Soup Search}.

:on-off:  Any p2 {oscillator} in which all {rotor} cells die from
   {overpopulation}.  The simplest example is a {beacon}.  Compare
   {flip-flop}.

:O-pentomino:  Conway's name for the following {pentomino}, a
   {traffic light} {predecessor}, although not one of the more common
   ones.
	*****

:orbit:  A term proposed by Jason Summers to refer to a natural
   stabilization of a {puffer}.  For example, the {switch engine} has
   two (known) orbits, the block-laying one and the glider-producing
   one.

:Orion: (c/4 diagonally, p4)  Found by Hartmut Holzwart, April 1993.
	...**.........
	...*.*........
	...*..........
	**.*..........
	*....*........
	*.**......***.
	.....***....**
	......***.*.*.
	.............*
	......*.*.....
	.....**.*.....
	......*.......
	....**.*......
	.......*......
	.....**.......
   In May 1999, Jason Summers found the following smaller variant:
	.**..........
	**...........
	..*..........
	....*....***.
	....***....**
	.....***.*.*.
	............*
	.....*.*.....
	....**.*.....
	.....*.......
	...**.*......
	......*......
	....**.......

:orphan:  Conway's preferred term for a {Garden of Eden}.  According to
   some definitions, an orphan consists of just the minimum living and
   dead cells needed to ensure that no parent is possible, whereas a GoE
   is an entire infinite Life plane that contains an orphan.

:Orthogonoid: (256c/3476016, p3476016)  A {self-constructing}
   {spaceship} analogous to the {Demonoid}s, with a slow orthogonal
   direction of travel.  The first example was completed by Dave Greene
   on 29 June 2017, with a top speed of 16c/217251 (this is just
   256c/3476016 in lowest terms).
     The construction recipe is a stream of MWSSes, with the recovery
   time limited to 90 ticks by the {Lx200} {dependent conduit} that
   follows the initial {syringe} converter.  The design is
   {hashlife}-friendly, meaning that the spaceship can be trivially
   adjusted so that spatial and temporal offsets are exact powers of
   two; period 4194304 and period 8388608 versions have been
   constructed, with speeds of c/16384 and c/32768 respectively.
     The MWSSes are converted to {Herschel}s, which produce a standard
   {single-channel} glider stream that runs the Orthogonoid's single
   construction arm.  After the child circuitry is complete, a
   previously constructed {Snark} in the parent is removed from the
   construction arm lane, converting it to a "destruction arm" that
   shoots down the previous constructor/reflector in the series.

:oscillator:  Any pattern that is a {predecessor} of itself.  The term
   is usually restricted to non-{stable} finite patterns; period 1
   oscillators are {stable} and are usually just called {still life}s.
   The {blinker} is the smallest non-stable oscillator, having period 2.
   There are oscillators of almost all higher periods (see
   {omniperiodic}).  In general {cellular automaton} theory the term
   "oscillator" usually covers {spaceship}s as well, but this usage is
   not normal in Life.
     Oscillators consisting of separate objects which do not react in
   any phase are usually ignored.  For example, a separated {blinker}
   and {pulsar} makes a period 6 oscillator, but is considered
   {trivial}.
     An oscillator can be divided into a {rotor} and a {stator}, and the
   stator can be further subdivided into {bushing} and {casing}.  Some
   oscillators have no casing cells, and a few 100%-{volatility}
   oscillators also have no bushing cells.
     An oscillator can be constructed from any {gun} as long as {eater}s
   can be added to consume its output.  If it is a {true} {gun} then the
   period of the oscillator will be the same as the gun - unless the
   eating mechanism multiplies the period, as in the case of gliders
   caught by a {boat-bit}.
     With the discovery of {reflector}s, {relay}s provide an easy way to
   create oscillators of all large periods.  For example, eight gliders
   travelling in a loop created by four {Snark}s can create any period
   above 42, with a population never exceeding 356 live cells.
     For the very lowest periods, whole families of {extensible}
   oscillators are known.  Examples of this are {barberpole}, {cross},
   {pentoad}, {p6 shuttle}, {snacker}, and {multiple roteightors}.  Any
   of the {shuttle}s are oscillators by definition, for example the
   {queen bee shuttle}.  Many of these are also extensible.  Other
   oscillators such as {figure-8} and {tumbler} have unique mechanisms
   that are not part of an extended family.
     Some oscillators are useful because of the {perturbation}s they can
   cause to other objects.  This is especially true if they provide a
   {spark} on their boundary.  Some oscillators are explicitly found by
   {search program}s in order to produce these sparks, such as
   {pipsquirter}s.
     Some higher period oscillators have been found while running random
   {soup}s.  This is especially true if the soup is run on a cylindrical
   or torus {universe}.  Sometimes the found objects can be moved to the
   normal universe and supported there by added {catalyst}s.
   {Achim's p144} is an example.

:Osqrtlogt: (p1 circuitry)  A pattern constructed by Adam P. Goucher in
   2010, which uses an unbounded triangular region as memory for a
   binary counter.  Empty space is read as a zero, and a boat as a one,
   as shown in the example pattern in {memory cell}.  The pattern's
   diametric growth rate is O(sqrt(log(t))), which is the slowest
   possible for any Life pattern, or indeed any 2D Euclidean cellular
   automaton.  The population returns infinitely often to its initial
   minimum value (during carry operations from 11111...1 to 100000...0,
   so it can be considered to be an unusual form of {sawtooth}.

:OTCA metapixel: (p46 circuitry)  A 2048 x 2048 period 35328 {metacell}
   constructed by Brice Due in 2006.  It contains a large "pixel" area
   that contains a large population of {LWSS}es when the metacell state
   is ON, but is empty when it is OFF.  This allows the state of the
   metacell to be visible at high zoom levels, unlike previous
   {unit cell}s where the state was signaled by the presence or absence
   of a single glider in a specific location.

:out of the blue:  See {natural Heisenburp}.  Other similar mechanisms,
   particularly the method of {LWSS} creation used in the pixel part of
   the {OTCA metapixel}, may also be referred to as "out of the blue"
   reactions.

:overclocking:  A term used when a {circuit} can accept a signal at a
   specific period which it cannot accept at a higher period.  A
   {syringe} is a simple example.
     Some {staged recovery} circuits also permit overclocking, and can
   function successfully at a rate faster than their {recovery time}.  A
   {Silver reflector} has a recovery time of 497 ticks, but can be
   overclocked to reflect a period 250 glider stream, or any nearby
   period above 248, simply by removing a beehive after the first glider
   enters the reflector.  However, a continuous stream of gliders is
   then required to maintain the circuit, with timing within a tightly
   bounded range.

:overcrowding:  = {overpopulation}

:over-exposure:  = {underpopulation}

:overpopulation:  Death of a cell caused by it having more than three
   {neighbour}s.  See also {underpopulation}.

:over-unity reaction:  An important concept in {gun} and
   {macro-spaceship} construction.  To be a good candidate for building
   one of these types of patterns with a new period or speed, a
   stationary reaction (for a gun) or a moving reaction (for a
   macro-spaceship) must be able to produce some number of output
   {signal}s, strictly greater than the number of input signals required
   to maintain the reaction.  The extra signal becomes a gun's output
   {stream}, or may be used in a variety of ways to construct the
   supporting {track} for a macro-spaceship.  By implication,
   "over-unity" refers to the ratio of output signals to input signals.
     If all signal outputs must be used up to sustain a stationary
   reaction, a high-period {oscillator} may still be possible.  See
   {emu} for example.

:overweight spaceship:  = {OWSS}

:OWSS:  A would-be {spaceship} similar to {LWSS}, {MWSS} and {HWSS} but
   longer.  On its own an OWSS is unstable, but it can be escorted by
   true spaceships to form a {flotilla}.

:Ox:  A 1976 novel by Piers Anthony which involves Life.

:p:  = {period}

:p1:  Period 1, i.e., {stable}.  In the context of logic {circuit}ry,
   this tends to mean that a mechanism is constructed from
   {Herschel conduit}s that contain only {still life}s as {catalyst}s.
   In the context of {slow glider construction}, a P1 {slow salvo} is
   one in which there are no constraints on the {parity} of gliders in
   the salvo, because the {intermediate target}s are all stable
   constellations.  (The usual alternative is a "P2 slow salvo", where
   the relative timing between adjacent gliders can be increased
   arbitrarily, but only by multiples of two ticks.)

:p104 gun:  A {glider gun} with period 104, found by Noam Elkies on 21
   March 1996.  It is based on an {R-pentomino} {shuttle} reaction.
	.**........**..........................
	.**.........*.......*..................
	.**.........*.**...*.*............**...
	.*...........*......*.............***..
	*.*......**......*................**.*.
	*.**.....**....*....................*.*
	................*..................*..*
	....................................**.
	.**....................................
	.**....................................
	...............**......................
	................**..................**.
	................*...................**.
	.**......***........................**.
	*..*.......*........................*..
	*.*.........................**.....*.*.
	.*.**.......................**.....*.**
	..***.............*....................
	...**............*.*...................
	..................*.................**.
	....................................**.

:p11 bumper: (p11)  A periodic {colour-preserving} {glider} {reflector}
   with a minimum {repeat time} of 44 ticks.  Unlike the p5 through p8
   cases where Noam Elkies' {domino}-spark based reflectors are
   available, no small period-22 {colour-changing} reflector is known.
   A {stable} {Snark} reflector can be substituted for any {bumper}.
   This changes the timing of the output glider, which can be useful for
   rephasing periodic glider streams.
	............................*..
	............................*.*
	............................**.
	...............................
	...............................
	...............................
	...............................
	...............................
	...............................
	...............................
	...............................
	.................*.............
	.................*.*...........
	.................**............
	...............................
	.........**....**..............
	.........**...*..*.............
	...**....**....*.*.............
	....*.....**....*..............
	..*.....*.**...................
	..**..***...........**.........
	.....*....*.*.......*..........
	..***.**.**.***......***.......
	.*....*....*...*.......*.......
	*.*.*...**.*..*................
	*.*......*.*.*.................
	.*..*****..**..................
	..**....*.*....................
	....****..*....................
	..**......**...................
	..*..*.........................
	....**.........................
     In practice this reflector is not useful with input streams below
   period 121, because lower-period bumpers can be used to reflect all
   smaller multiples of 11 for which the bumper reaction can be made to
   work.

:p130 shuttle:  A {shuttle} found in March 2004 by David Eppstein, which
   originally needed several period 5 oscillators for support.  David
   Bell found a reaction between two of the shuttles to produce a p130
   glider gun.  On 18 November 2017 Tanner Jacobi found that the
   {stable} {sidesnagger} can be used to support the shuttle instead,
   and this is shown here.
	.....**................................**.....
	.....**................................**.....
	..............................................
	..............................................
	.........................*....................
	**....**..................*...........**....**
	**...*..*................**..........*..*...**
	.....*.*...........*******............*.*.....
	......*...........***..*...............*......
	..................*..**.*.....................
	...*..................*.*.................*...
	..*.*...............**.**................*.*..
	..**................****..................**..
	..............................................
	..**................****..................**..
	..*.*...............**.**................*.*..
	...*..................*.*.................*...
	..................*..**.*.....................
	......*...........***..*...............*......
	.....*.*...........*******............*.*.....
	**...*..*................**..........*..*...**
	**....**..................*...........**....**
	.........................*....................
	..............................................
	..............................................
	.....**................................**.....
	.....**................................**.....

:p144 gun:  A {glider gun} with {true} period 144.  The first one was
   found by Bill Gosper in July 1994.  For a full description and
   pattern see {factory}.

:p14 gun:  A glider gun which emits a period 14 glider stream.  This is
   the smallest possible period for any stream, so such a gun is of
   great interest.  There is no known true-period p14 glider gun, and
   finding a small direct example is well beyond current search
   algorithms' abilities.  However, pseudo-period p14 guns have been
   created by {inject}ing gliders into a higher period glider stream.
   The first pseudo p14 gun was built by Dieter Leithner in 1995.
   Smaller pseudo p14 guns have since been constructed, but they are
   still much too large to show here.  The essential mechanism used by
   them is demonstrated in {GIG}.

:p15 bouncer:  Noam Elkies' {colour-changing} glider reflector, with
   {Karel's p15} providing the necessary {domino} {spark}.  Compare to
   the {colour-preserving} {Snark}.  The minimum {repeat time} is 30
   ticks.
	........................*..
	........................*.*
	........................**.
	...........................
	...........................
	...........................
	...........................
	.................*.........
	................*..........
	................***........
	...........................
	...**....**.........**.....
	..*..*..*..*....**..**.....
	..**......**...*.*.........
	..**......**....*..........
	....**..**.................
	..................**.......
	..................*........
	...................***.....
	.*..*.**.*..*........*.....
	**..*....*..**.............
	.*..*.**.*..*..............

:p15 bumper:  A periodic {colour-preserving} {glider} {reflector} with
   {Karel's p15} providing the necessary {spark}.  The minimum
   {repeat time} is 45 ticks.  For an equivalent {colour-changing}
   periodic glider reflector see {p15 bouncer}.  A {stable} {Snark}
   reflector can be substituted for any {bumper}.  This changes the
   timing of the output glider, which can be useful for rephasing
   periodic glider streams.
	............................*.*
	............................**.
	.............................*.
	...............................
	...............................
	...............................
	...............................
	...............................
	...............................
	...............................
	...............................
	.................*.............
	.................*.*...........
	.................**............
	...............................
	...............**..............
	.**.**.**.....*..*.............
	.**....**......*.*.............
	.**.**.**.......*..............
	...............................
	....**..............**.........
	..*....*............*..........
	.*......*............***.......
	*........*.............*.......
	*........*.....................
	*........*.....................
	.*......*......................
	..*....*.......................
	....**.........................

:p15 reflector:  An ambiguous term that may refer to
   {PD-pair reflector}, {p15 bouncer}, or the more recently discovered
   {p15 bumper}.

:p184 gun:  A {true} period 184 {double-barrelled} glider gun found by
   Dave Buckingham in July 1996.  The {engine} in this gun is a
   {Herschel descendant}.  Unlike previous glider guns, the reaction
   flips on a diagonal so that both gliders travel in the same
   direction.
	...................*...........
	.................***...........
	................*..............
	................**.............
	..............................*
	............................***
	...........................*...
	...........................**..
	...............................
	...............................
	...............................
	...............................
	....................**.........
	...................*.*.........
	...................*...........
	...................**.*........
	..**.................**........
	.*.*...........................
	.*.............................
	**.............................
	...............................
	...............................
	...............................
	...............................
	...............................
	...............................
	...............................
	......**.......................
	.....*.*.......................
	.....*.........................
	....**.........................

:p1 megacell: (p1 circuitry)  A {metacell} constructed by Adam P.
   Goucher in 2008, capable of being programmed to emulate any Moore
   neighborhood rule, including isotropic and anisotropic non-totalistic
   rules.  It fits in a 32768 by 32768 bounding box, with the resulting
   metacell grid at 45 degrees to the underlying Life grid.  Like the
   {OTCA metapixel}, it includes a large "pixel" area so that the state
   of the megacell can easily be seen even at extremely small-scale zoom
   levels.

:p1 telegraph: (p1 circuitry)  A variant of Jason Summers' {telegraph}
   pattern, constructed in 2010 by Adam P. Goucher using only stable
   circuitry.  A single incoming glider produces the entire ten-part
   composite lightspeed signal that restores the beehive-chain
   {lightspeed wire} to its original position.  The signal is detected
   at the other end of the telegraph and converted back into a single
   output signal.  This simplification came at the cost of a much slower
   transmission speed, one bit per 91080 ticks.  In this mechanism,
   sending the entire ten-part signal constitutes a '1' bit, and not
   sending the signal means '0'.  See also {high-bandwidth telegraph}.

:p22 gun:  A {true} period 22 {glider gun} constructed by David Eppstein
   in August 2000, using two interacting copies of a p22 oscillator
   found earlier the same day by Jason Summers.
	..................**.........................
	...................*.......*.................
	...................*.*..............**.......
	....................**............**..*......
	........................***.......**.**......
	........................**.**.......***......
	........................*..**............**..
	.........................**..............*.*.
	...................................*.......*.
	...........................................**
	.............................................
	**...........................................
	.*...........................................
	.*.*.............***.........................
	..**...*........*...*........................
	......*.**......*....*.......................
	.....*....*......**.*........................
	......*...*........*...**....................
	.......***.............*.*...................
	.........................*...................
	.........................**..................

:p246 gun:  A {true} period {glider gun} with period 246, discovered by
   Dave Buckingham in June 1996.  The 180-degree mod-123 symmetry of its
   {bookend}-based {engine} makes it trivial to modify it into a
   {double-barrelled} gun.  Its single-barreled form is shown below.
	..................................*........
	..................................***......
	................................**...*.....
	...............................*.*.**.*....
	..............................*..*..*.*....
	....................................*.**...
	..................................*.*......
	................................*.*.*......
	.................................**.**.....
	...........................................
	**.........................................
	.*.........................................
	.*.*.................**....................
	..**..................*..................**
	....................*.*..................*.
	....................**.................*.*.
	.......................................**..
	...........................................
	...........................................
	...........................................
	...........................................
	...........................................
	...........................................
	.............................**............
	.......................*.....**............
	.................**.***....................
	.................*..****...................
	.................*.**......................
	...........................................
	...........................................
	.....*.....................................
	....*.****.................................
	...*.*.***.................................
	..*.*......................................
	...*.......................................
	...**......................................
	...**......................................
	...**......................................

:p24 gun:  A {glider gun} with {true} period 24.  The first one was
   found by Noam Elkies in June 1997.  It uses three p4 {oscillator}s to
   {hassle} a pair of {traffic light}s.  One of the oscillators was very
   large and custom-made.  Shown below is a much smaller version built
   by Jason Summers and Karel Suhajda in December 2002, using the same
   mechanism but with a smaller oscillator:
	.......................*..*................
	.....................******................
	.................**.*........*.............
	.............**.*.*.*.********..*..........
	...........***......*.*...*...***..........
	..........*....*..*.*...*...**.............
	...........*****..*.****.*...*.**..........
	............*....**.....*.*.**..*....**.*..
	..........*...**...*.**..**..**.....*.**.*.
	..........*****.****.*..............*....*.
	.....................*........*..**.*.**.**
	............***...***...*.*......*.*.*.*.*.
	...........*......*....*..*.*.*....*.*.*.*.
	............**..*.*.......*..**...*.*.**.**
	**.**..................**.**.***..*...*.*..
	.*.*......*...*.*.*....*..*.............*..
	*..*..*..*.*...*.***...*.*........*.*.**...
	***.**.*.***...........*.........**........
	...*.*.*.**......................*.........
	..*.**...*.*..............**.....*..*......
	.*...**....*.............***.....*.........
	.**.......**..............**.....**........
	..........**......***.............*.*.**...
	.**.......**......*.*...................*..
	.*...**....*......***.............*...*.*..
	..*.**...*.*......................*.*.**.**
	...*.*.*.**........................*.*.*.*.
	***.**.*.***.....................*.*.*.*.*.
	*..*..*..*.*.........**..........**.*.**.**
	.*.*......*..........*..............*....*.
	**.**.................***...........*.**.*.
	........................*............**.*..

:p256 gun:  A {true} period 256 four-barrelled {glider gun} found by
   Dave Buckingham in September 1995.  It uses four {R64} {conduit}s to
   make the second smallest known {Herschel loop} (after the
   {Simkin glider gun}).  The p256 gun was an early "teaser" from Dave
   Buckingham before he released his full {Herschel} {technology}.
	...............................**................
	...............................**.....**.........
	......................................**.........
	.................................................
	.................................................
	.......**........**.................**...........
	.......**.........*.................**...........
	..................*.*.....................**.....
	...................**.....................**.....
	.**..............................................
	.**..............................................
	.....**..........................................
	.....**...............*..........................
	......................*.*........................
	......................***........................
	........................*........................
	**...............................................
	**.........................................**....
	...........................................*.....
	.........................................*.*.....
	.........................................**......
	.................................................
	.................................................
	.................................................
	.................................................
	.................................................
	.................................................
	.................................................
	.................................................
	.................................................
	.................................................
	......**.......................................**
	......*........................................**
	.......*.........................................
	......**.........................................
	......................*.*........................
	.......................**.................**.....
	.......................*..................**.....
	..............................................**.
	..............................................**.
	.....**..........................................
	.....**..........................................
	...........**...........................**.......
	...........**...........................**.......
	.................................................
	.................................................
	.........**......................................
	.........**.....**...............................
	................**...............................
   Either {eater}s or {snake}s can be added as shown above, to suppress
   three of the glider streams so that only one stream escapes.  This
   gun's p256 glider stream is well-suited for repeated reactions with
   receding {Cordership}s, or for "Hashlife-friendly" {signal}
   {circuit}ry.

:p29 pentadecathlon hassler:  A {hassler} where two copies of a period
   29 oscillator (which is itself a {pre-pulsar} hassler) change the
   period of a {pentadecathlon}.
	..........*.......*....................*.......*..........
	.........*.*.....*.*..................*.*.....*.*.........
	..........*.......*....................*.......*..........
	..........................................................
	..........................................................
	..........................................................
	.........................**....**.........................
	.........................***..***.........................
	...**....................**....**....................**...
	...*.......*.....*......................*.....*.......*...
	**.*......***...***....................***...***......*.**
	*..**.....***...***....................***...***.....**..*
	.**....*.............**............**.............*....**.
	...*****.............*.*..........*.*.............*****...
	...*....**.............*..........*.............**....*...
	....**..*.......**.....**........**.....**.......*..**....
	......*.*.......**......................**.......*.*......
	......*.*.*..*..............................*..*.*.*......
	.......**.****..............................****.**.......
	.........*......................................*.........
	.........*.*..................................*.*.........
	..........**..................................**..........

:p30 gun:  A {glider gun} with {true} period 30.  The first one, found
   by Bill Gosper in November 1970 (see {Gosper glider gun}), was also
   the first gun found of any period.  All known p30 glider guns are
   made from two or more interacting {queen bee shuttle}s. Paul Callahan
   found 30 different ways that three {queen bee shuttle}s can react to
   form a period 30 glider gun.  One of the most interesting of these is
   shown below in which the gliders emerge in an unexpected direction.
	**...................................
	.*...................................
	.*.*......*.............*............
	..**......****........*.*............
	...........****......*.*.............
	...........*..*.....*..*.............
	...........****......*.*.............
	..........****........*.*........**..
	..........*.............*........*.*.
	...................................*.
	...................................**
	.....................................
	................***..................
	...............**.**.................
	...............**.**.................
	...............*****.................
	..............**...**................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	..............**.....................
	...............*.....................
	............***......................
	............*........................

:p30 reflector:  = {buckaroo}

:p30 shuttle:  = {queen bee shuttle}

:p36 gun:  A glider gun with {true} period 36.  The first one was found
   by Jason Summers in 2004.  Shown below is a smaller version using
   improvements by Adam P. Goucher and Scot Ellison:
	................................................*.
	..............................................***.
	.............................................*....
	.............................................**...
	..................................................
	..................................................
	..................................................
	..................................................
	..................................................
	..................................................
	.................................**...............
	................................*..*..............
	................................*.*.*.............
	.................................*..***...........
	..................................................
	...................................**.....**......
	...................................*.....*.**.....
	.........................................*..*.....
	..........................................***.....
	......................................**..**......
	.....................................***..........
	.....................................*..*.........
	.....................................**.*.....*...
	......................................**.....**...
	..........................**......................
	**.......................*..*..............***..*.
	.*........................*.*................*.*.*
	.*.*..................**...*..................*..*
	..**..........*........*.**....................**.
	.............**..........*........................
	............**.*.........*........................
	.............*.*..................................
	..............**..................................
	.......................**.........................
	.......................*.*........................
	.............*.........*.**.......................
	.............*..........**........................
	............**.*........*.........................
	...........*...**.................................
	..........*.*.....................................
	..........*..*....................................
	...........**...........*...........**............
	.......................*.*...........*............
	.......................*.*..*********.............
	....................**.*..*.*******..***..........
	....................**.*....******..*..*..........
	.......................*.............**...........
	.......................*.*....**..................
	........................**....**..................

:p3 bumper:  A variant of Tanner Jacobi's {bumper} found by Arie Paap in
   April 2018.  Two forms of the period 3 {oscillator} {catalyst} are
   shown below.
	..*........................*..................
	*.*......................*.*..................
	.**.......................**..................
	......................*.......................
	....................***.......................
	...................*..........................
	...................**.........................
	..................**..........................
	.......**........**.............**.........**.
	......*..*....*...*............*..*....*.****.
	......*.*...***.***............*.*...***..*.*.
	.......*.........*..............*.............
	............******...................***......
	..**........**.*...........**.......*.***.*.**
	...*.......**...............*......*....*.**.*
	***......................***.......**..***....
	*........................*............*...***.
	.......................................***..*.
	.........................................*....
     For bounding box optimization purposes, it's also possible to
   replace the {eater1} in a p3, p6 or p9 bumper with another period 3
   oscillator, saving one row along the south edge at the cost of a
   higher population.
	....*.........................
	..*.*.........................
	...**.........................
	..............................
	..............................
	..............................
	..............................
	..............................
	.............................*
	......*......*.............***
	.*...*.*...*.*............*...
	*.*..*.*....**.............*..
	*.***.*.................*..*..
	.*..**........**........*.....
	..***........*..*....***..*...
	.............*.*....****.*....
	....***.......*...............
	...*..*............*..*.*.....
	...*****.**...........*.......
	.*.*...**.*.......***.........
	.**......*....................
     The {repeat time} for all these variants is 36 ticks, as shown.

:p44 gun:  A {glider gun} with a {true} period of 44.  The first one was
   found by Dave Buckingham in April 1992.  It uses two interacting
   copies of an {oscillator} which he also found.  In 1996 he found a
   gun which only used one copy of the oscillator.  Paul Callahan
   improved it in 1997, resulting in the gun shown below:
	.................**......**.................
	.................**......**.................
	............................................
	............................................
	............................................
	............................................
	............................................
	............................................
	.**......................................**.
	*.*......................................*.*
	*.*.**................................**.*.*
	.*.*.*................................*.*.*.
	...*....................................*...
	..*..*.............*....*.............*..*..
	..*...............**....**...............*..
	..*...*..........*........*..........*...*..
	..*...*...........**....**...........*...*..
	..*................*....*................*..
	..*..*................................*..*..
	...*....................................*...
	.*.*.*................................*.*.*.
	*.*.**................................**.*.*
	*.*......................................*.*
	.**......................................**.
	............................................
	............................................
	............................................
	...............**...........................
	................*...........................
	.............***............................
	.............*....................**........
	..................**..............*.*.......
	..................**................*.......
	....................................**......
	............................................
	............................................
	............................................
	....................**......................
	...................*.*......................
	...................*........................
	..................**........................

:p44 MWSS gun:  A gun discovered by Dieter Leithner in April 1997, in a
   somewhat larger form.  This was the smallest known gliderless gun and
   smallest known MWSS gun until the construction in 2017 of the gun
   shown under {gliderless}, based on {Tanner's p46}.
     The p44 MWSS gun is based on a p44 oscillator discovered by Dave
   Buckingham in early 1992, shown here in an improved form found in
   January 2005 by Jason Summers using a new p4 {sparker} by Nicolay
   Beluchenko.  A glider shape appears in this gun for three consecutive
   generations, but always as part of a larger {cluster}, so even a
   purist would regard this gun as gliderless.
	.......*..........................................
	..**...*.*....*...................................
	..*..**..*.*.**.*..***..**........................
	....**.......**.*.*.**..**........................
	...***.......*.......***.........*................
	.......................*.......***................
	.......................*......*........***........
	..............................**.......*..*.......
	.........**..............*.............*..........
	.........**.............*..............*...*......
	.........................**............*..........
	........................*.*.............*.*.......
	..................................................
	.......................*.*.....***................
	........................*.....*..*..............**
	**............***.......*......**...........**.*.*
	**...........*...*..........................**.*..
	.............**.**..............................*.
	.................................**.........**.**.
	..............................**.............*.*..
	.............................................*.*..
	..............................................*...
	.............**.**.............*.*................
	**...........*...*.............**.................
	**............***.................................
	...........................**.....................
	...........................*.*....................
	.............................*....................
	.............................**...................
	..................................................
	.........**.......................................
	.........**.......................................
	..................................................
	.......................*..........................
	.......................*..........................
	...***.......*.......***..........................
	....**.......**.*.*.**..**........................
	..*..**..*.*.**.*..***..**........................
	..**...*.*....*...................................
	.......*..........................................

:p45 gun:  A {true}-period glider gun discovered by Matthias Merzenich
   in April 2010.  By most measures this is the smallest known
   odd-period gun of any type, either true-period or {pseudo}-period:
	...............*..*..*..........................
	...............*******..........................
	................................................
	...............*******..........................
	...............*..*..*..........................
	................................................
	................................................
	................................................
	................................................
	................................................
	................*..*............................
	............**..*..*............................
	............**..*..*.......**...................
	...........................**....**...*..*...**.
	.................................*****....*****.
	.................................**...*..*...**.
	...........................***..................
	................................................
	**.**...........................................
	.*.*.......................***..................
	.*.*......***...................................
	**.**.............................*.*...........
	.*.*...............................**...........
	.*.*......***......................*............
	**.**...........................................
	................................................
	...........**...................................
	...........**.......*..*..**....................
	....................*..*..**....................
	....................*..*........................
	................................................
	................................................
	...............................................*
	.............................................*.*
	..............................................**
	..................*..*..*.......................
	..................*******.......................
	................................................
	..................*******.......................
	..................*..*..*.......................

:p46 gun:  A glider gun which has true-period 46.  The first one found
   was the {new gun} by Bill Gosper in 1971.  Prior to the discovery of
   {Tanner's p46} in October 2017, all known p46 guns were made from two
   or more {twin bees shuttle}s that interact (e.g., see
   {twin bees shuttle pair}). See {edge shooter} and {double-barrelled}
   for two more of these.
     On 21 October 2017 Heinrich Koenig found a glider gun using two
   copies of {Tanner's p46} placed at right angles to each other.  This
   is the first p46 gun found which makes no use of the
   {twin bees shuttle}.
	....**.............................
	.....*.............................
	.....*.*...........................
	......**..**.......................
	..........**.......................
	...................................
	...................................
	...................................
	...................................
	...................................
	...................................
	*..................................
	***.......**.......................
	...*......*.*......................
	..*.*.......*......................
	..**......*.*......................
	..........**.......................
	..**...............................
	..*................................
	...***.............................
	.....*.............................
	........**.........................
	.........*.........................
	......***..............***.........
	......*...............*...*........
	.....................*.....*.......
	.............**......*.....*.......
	.............**......***.***.......
	...............................**..
	...............................*.*.
	............**...................*.
	.............*...................**
	..........***................**....
	..........*.............*....*.....
	.......................*.*.*.*.....
	......................*.**.**......
	......................*............
	.....................**............
     See {gliderless} for a {MWSS} gun also made using two copies of
   Tanner's p46.

:p46 shuttle:  = {twin bees shuttle}

:p48 gun:  A {true} period compound {glider gun} based on the {p24 gun},
   using a {Rich's p16} {oscillator} as a {filter} to remove half of the
   gliders from the {stream}.
	.................**...........**.............
	................*..*.........*..*............
	................*.*...**.**...*.*............
	..............**..*.*.......*.*..**..........
	...............*.*.*....*....*.*.*...........
	..............*..**..*******..**..*..........
	..............**.....*.*.*.*.....**..........
	.......................*.*...................
	.....*..**.........***.....***...............
	....*.*..*..*.....*.*.*...*.*.*..............
	....*.**.*.*.*....**..*****..**..............
	...**.*..*.*..*..............................
	...*..*.**..*................................
	....***.*.*...***............................
	......**.*.....**............................
	..*.*..*.*...*..*....*.*.*...................
	..**..**.*.**..***....***.............**.....
	........**.*...**......*.............*..*....
	..*****....*........................**.......
	.*....*.***.................**.....***.....*.
	.*.**.*.*......**.......*...*.*....*..*...*.*
	**.*..*......****........*....*.....***...**.
	.*.*.*.*.....**..*.....***....**.............
	.*.*.**.*..*........................***...**.
	**.**..**...****...................*..*...*.*
	...*..***..*..**....*..............***.....*.
	...*.*.**.....*....*.*........*.....**.......
	..**.*..**.*..*...*...*........*.....*..*....
	....*...**..*..*...*.*.......***......**.....
	....*.*.......*.....*........................
	...**.**..........***........................
	..........**....*******....**................
	..........*..*..**.*.**..*..*................
	...........**.****...****.**.................
	........***..*...........*..***..............
	.......*...**.**.......**.**...*.............
	.......**.*...**.......**...*.**.............
	........*.***...*.....*...***.*..............
	.......*......**.......**......*..........*..
	........******...........******............*.
	..........*..*...........*..*............***.

:p4 bumper: (p4)  A periodic {colour-preserving} {glider} {reflector}
   with a minimum {repeat time} of 36.  Unlike the p5 through p8 cases
   where Noam Elkies' {domino} spark-based reflectors are available, no
   small period-4 {colour-changing} reflector is known.  A {stable}
   {Snark} reflector can be substituted for any {bumper}.  This changes
   the timing of the output glider, which can be useful for rephasing
   periodic glider streams.
	.....................*..
	.....................*.*
	.....................**.
	........................
	........................
	........................
	........................
	........................
	........................
	............*...........
	............*.*.........
	............**..........
	........................
	....**....**............
	...*..*..*..*...........
	..........*.*...........
	...........*............
	..*..*..................
	..*.**.........**.......
	...*.***.......*........
	***...*.*.......***.....
	*.......*.........*.....
	........**..............

:p4 reflector:  The following {glider} {reflector}, discovered by Karel
   Suhajda in October 2012.  Its minimum repeat time is 52 ticks.
   Unlike the various {bouncer}s discovered many years earlier, it is a
   {colour-preserving} reflector, so it was made obsolete the following
   year by the discovery of the much smaller stable {Snark}, which uses
   the same initial {bait} reaction and so produces an output glider
   with the same timing.  For a smaller periodic {colour-preserving}
   glider reflector with a different output timing, see {p4 bumper}.
	................................*.........................
	...............................*..........................
	...............................***.......*.*..............
	........................................*.**..............
	......................................***.....*...........
	.....................................*...********.........
	..................................*.*.*..*.......*........
	..............*...................****.**.*******.*.......
	..............***..................***.....*.*..*.*..**...
	.................*...................***.*.*...**.*.*.*...
	................**.............***..**.*****....*.*.*.....
	.............................*.*...***.**.*..*.****..*..**
	...........................**.....*....*..*..*...*....*..*
	...................*.......**.*.*..*......*..*....*******.
	..................*...........*.*..*..*..*.........*......
	..................***........*....*..*...........*...**...
	............................*.*******........**.*.***.*...
	.............................*.........*.*....*.*.*.......
	...................**..........*********.***..*.*.........
	...................**.......*...*.......*...*.*.*.........
	...........................*..*...****..*..*.*.*..........
	.............................**...*...*.*.*..*............
	.............................*.....***.*.*.**..*..........
	........**...............*...***.....*...*...***..........
	...**..*..*..................*...**..*..*.**..............
	...*....*.*..................*...****...*.*.**............
	**.*.....*................***...*......**...*.*...........
	.*.*.**....................***.....*..**..*.*.*...........
	*..*..*........**...........***..***.***..*.*.**..........
	**..*....*.....*.*..........*..*...*...*..*.*.............
	.....*****.......*...........*.*..*.**...****.............
	................*..........*.*.*.***.***.*................
	.......*.........***......*.**.*..**......................
	......*.*..........*......*.....*......**.*...............
	.......*...................*****......*..**...............
	.............................*........**..................

:p54 shuttle: (p54)  A surprising variant of the {twin bees shuttle}
   found by Dave Buckingham in 1973.  See also {centinal}.
	**.........................**
	.*.........................*.
	.*.*.......*.............*.*.
	..**.....*..*.....*......**..
	............*.....**.........
	........*..........**........
	........*...**....**.........
	.........*****...............
	.............................
	.........*****...............
	........*...**....**.........
	........*..........**........
	............*.....**.........
	..**.....*..*.....*......**..
	.*.*.......*.............*.*.
	.*.........................*.
	**.........................**

:p5 bouncer: (p5)  A {colour-changing} glider reflector constructed by
   Noam Elkies in September 1998 by welding together two special-purpose
   period-5 {sparker}s.  The minimum {repeat time} is 25 ticks.  For
   {colour-preserving} glider reflectors see {p5 bumper} and the
   {stable} {Snark} reflector.
	..........................*..
	........................**...
	.........................**..
	.............................
	.............................
	........**...................
	.....*..*.*........*.........
	....*.*.*.*.......*..........
	...*.*.*..**......***........
	...*...*.*..*................
	**.**..*.*.*..........**.....
	*.*....***..*.....**..**.....
	..*.***...**.....*.*.........
	..*..*.....*......*..........
	...*...*.*..*............**..
	....***.**.**.......**....*..
	......*....*........**..***..
	.......***.*.....**.....***..
	..........*.**...**.....**...
	.........*..*..***.*........*
	.........**..***...........**
	................*............
	.............****.*..........
	............*..*...*.........
	............**...*.***.......
	.............*.*..*...*......
	.............*.**.*..**......
	..............*..*...........
	...............**............

:p5 bumper:  A periodic {colour-preserving} {glider} {reflector} with a
   {middleweight volcano} producing the necessary {spark}.  The minimum
   {repeat time} is 35 ticks.  For an equivalent {colour-changing}
   periodic glider reflector see {p5 bouncer}.  A {stable} {Snark}
   reflector can be substituted for any {bumper}.  This changes the
   timing of the output glider, which can be useful for rephasing
   periodic glider streams.
	............................*
	..........................**.
	...........................**
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	...**..*..........*..........
	...*..*.*.........*.*........
	....*.*.*.........**.........
	...**.*.**...................
	..*...**..*.....**...........
	.*..**...***...*..*..........
	.*.*.**..***....*.*..........
	..*.**...***.....*...........
	......**..*..................
	*****.*.**...........**......
	*..*..*.*............*.......
	.....*..*.............***....
	......**................*....

:p5 reflector:  Traditional name for {p5 bouncer} before 2016, but with
   the discovery of the {p5 bumper} this has become an ambiguous
   reference.

:p60 gun:  A glider gun with a {true} period of 60.  The first one was
   found by Bill Gosper in 1970 and is shown below.
	............................*..........
	............................*.*........
	...........**..................**......
	.........*...*.................**....**
	...**...*.....*................**....**
	...**..**.*...*.............*.*........
	........*.....*.............*..........
	.........*...*.........................
	...........**..........................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	..........*.*..........................
	.........*..*...**.....................
	**......**.....***.**..**..............
	**....**...*...*...*...*.*.............
	........**.....*.*........*............
	.........*..*..**......*..*............
	..........*.*.............*............
	.......................*.*.......**....
	.......................**........*.*...
	...................................*...
	...................................**..
   There are several other ways to create a p60 gun from two p30 guns
   using period-doubling reactions similar to the one shown here.

:p690 gun:  A {true} period 690 {glider} gun found by Noam Elkies in
   July 1996.  It is composed of a p30 {queen bee shuttle pair} and a
   p46 {twin bees shuttle} whose sparks occasionally react with each
   other.  This is a very compact gun for such a high period and is used
   in many patterns requiring sparse glider streams.
	...........*........................................
	...........***......................................
	..............*.....................................
	.............**.....................................
	....................................................
	....................................................
	....................................................
	....................................................
	...............***..................................
	..............*...*.................................
	....................................................
	.............*.....*................................
	.............**...**................................
	....................................................
	..........................................**.*......
	................*......**............***..**..*.....
	**.............*.*.....**.............**......*...**
	.*.............*.*.....................***...****..*
	.*.*.....*.....*........................*...*...***.
	..**...*.*.....*........*.....*.....................
	......*.*......*..*.....*.....*.........*...*...***.
	.....*..*......*..*....................***...****..*
	......*.*.......**..**...........**...**......*...**
	.......*.*...........................***..**..*.....
	.........*..............*.....*...........**.*......
	........................*.....*.....................

:p6 bouncer: (p6)  Noam Elkies' {colour-changing} glider reflector using
   the {p6 pipsquirter}, with a minimum {repeat time} of 24 ticks.  For
   {colour-preserving} glider reflectors see {p6 bumper} and the
   {stable} {Snark} reflector.
	.......................*.
	......................*..
	......................***
	...**....................
	...*.....................
	.....*...................
	....****.........*.......
	...*....*.......*........
	...*****.*......***......
	.**....*.*...............
	*..*.....**.........**...
	**.*.*.*..*.....**..**...
	...*..*.***....*.*.......
	...**.*...*.....*........
	.....*.*.**..............
	.....*.*.*........**.....
	......*..*........*......
	.......**..........***...
	.....................*...
:p6 bumper: (p6)  A periodic {colour-preserving} {glider} {reflector}
   with a {unix} providing the necessary {spark}.  The minimum
   {repeat time} is 36 ticks.  For an equivalent {colour-changing}
   periodic glider reflector see {p6 bouncer}.  A {stable} {Snark}
   reflector can be substituted for any {bumper}.  This changes the
   timing of the output glider, which can be useful for rephasing
   periodic glider streams.
	.......................*..
	.......................*.*
	.......................**.
	..........................
	..........................
	..........................
	..........................
	..........................
	..........................
	..............*...........
	..............*.*.........
	..............**..........
	..........................
	............**............
	.....**....*..*...........
	.....**.....*.*...........
	.............*............
	..........................
	.....***.........**.......
	**..*.**.........*........
	**..**............***.....
	....**..............*.....

:p6 pipsquirter: (p6)  A {pipsquirter} oscillator found by Noam Elkies
   in November 1997, used in various {hassler}s and the colour-changing
   {p6 bouncer}.
	.....*.........
	.....*.........
	...............
	...*...*.......
	.***.*.***.....
	*...**....*....
	*.**..**.*.*...
	.*..**..**.*...
	..**..**.*.*.**
	....*..*.*.*.**
	....****.**....
	........*......
	......*.*......
	......**.......

:p6 reflector:  Traditional name for {p6 bouncer} before 2016, but with
   the discovery of the {p6 bumper} this has become an ambiguous
   reference.

:p6 shuttle: (p6)  The following oscillator found by Nicolay Beluchenko
   in February 2004.
	*.............
	***...........
	...*..........
	..**..........
	..............
	......*.......
	.....****.....
	......*..*....
	.......***....
	..............
	..........**..
	..........*...
	...........***
	.............*
   This is {extensible} in more than one way:
	*........................
	***......................
	...*.....................
	..**.....................
	.........................
	......*..................
	.....****................
	......*..*...............
	.......***...............
	.........................
	..........***............
	..........*..*...........
	...........****..........
	.............*...........
	.........................
	.................*.......
	................***......
	.................*.*.....
	.................*.*.....
	..................**.....
	.....................**..
	.....................*.*.
	.......................*.
	.......................**

:p72 quasi-shuttle: (p72)  The following {oscillator}, found by Jason
   Summers in August 2005.  Although this looks at first sight like a
   {shuttle}, it isn't really.
	..............................*......
	.............................**......
	............................*.**.....
	.****......................***..*....
	*....*.......................*.*.*...
	*...*.*.......................*.*.*..
	.*...*.*......**...............*..***
	.......*.....*.*................**.*.
	.......*.....*...................**..
	....*..*.....***.................*...
	.....**..............................
	.....................................
	.....**..............................
	....*..*.....***.................*...
	.......*.....*...................**..
	.......*.....*.*................**.*.
	.*...*.*......**...............*..***
	*...*.*.......................*.*.*..
	*....*.......................*.*.*...
	.****......................***..*....
	............................*.**.....
	.............................**......
	..............................*......

:p7 bouncer: (p7)  Noam Elkies' {colour-changing} {glider} {reflector}
   using a {p7 pipsquirter}, with a minimum {repeat time} of 28 ticks.
   A high-{clearance} version is shown in {p7 pipsquirter}.  For
   {colour-preserving} glider reflectors see {p7 bumper} and the
   {stable} {Snark} reflector.
	.......................*.
	......................*..
	......................***
	.........................
	.........................
	.........................
	.........................
	................*........
	......**.......*.........
	......*.*......***.......
	........*................
	...*..*.**.........**....
	...****..*.....**..**....
	.......***....*.*........
	...****..*.....*.........
	..*...*.**...............
	.*.****.*........**......
	.*.*..*.*........*.......
	**.*.*.*.**.......***....
	*..***.*..*.........*....
	..*...*.*................
	...**.*.**...............
	....*....................
	..*.*.****...............
	.*.****..*...............
	.*.....*.................
	..******.*...............
	....*...*.*..............
	.......*..*..............
	........**...............

:p7 bumper: (p7)  A periodic {colour-preserving} {glider} {reflector}
   with a minimum {repeat time} of 35 ticks.  For an equivalent
   {colour-changing} periodic glider reflector see {p7 bouncer}.  A
   {stable} {Snark} reflector can be substituted for any {bumper}.  This
   changes the timing of the output glider, which can be useful for
   rephasing periodic glider streams.
	......*..................
	....*.*.......**.....**..
	.....**......*..*...*..*.
	.........................
	.......**.......*...*....
	......*..*....*.......*..
	......*.*.....**.....**..
	.......*.........*.*.....
	.............*..**.**..*.
	..**........*.*..*.*..*.*
	...*........*..*.*.*.*..*
	***.............*...*....
	*........................

:p7 pipsquirter:  A {pipsquirter} oscillator found by Noam Elkies in
   August 1999, used in various {hassler}s and the colour-changing
   {p7 reflector}.
	................*.....
	........*.......*.....
	.**...***..*..........
	..*..*...***..*...*.**
	..*.*.**....***.*.**.*
	**..*.*.****....*.....
	.*.**........***.****.
	.*....*.*.**...*.*..*.
	**.*.*.**....*.*......
	.*.*......****.*......
	.*..******....*.......
	**....*..*..*.........
	............**........
     A larger period-7 pipsquirter is used in cases where space is
   limited where the reflector should extend southward for as short a
   distance as possible:
	.....**..................................
	......***................................
	....*....*...............................
	..******.*.............................*.
	.*.....*.**....**.....................*..
	.*.**.*....*..*.*.....................***
	..*...*.**.*..*..........................
	....*.*..*.**.*..........................
	...**...*.....**.........................
	..*..**.*.****..*...**...................
	*..*...*.*...*.*...*.*..........*........
	**.*...*..**.*..****..**.......*.........
	.*.*.**.*.*.*.*.*...**..*......***.......
	*..***..*.....*....*..*.*................
	*.*...*.**...**....*.**.**.........**....
	.*.****..*..*.*....*.....*.....**..**....
	...*...*......**...*..****....*.*........
	...*.**..*..*.*....*.....*.....*.........
	....*.*.**...**....*.**.**...............
	......*.*.....*....*..*.*........**......
	......*.*...*.*.*...**..*........*.......
	.......*...*.*..****..**..........***....
	...........*.*.*...*.*..............*....
	............**.**...**...................

:p7 reflector:  Traditional name for {p7 bouncer} before 2016, but with
   the discovery of the {p7 bumper} this has become an ambiguous
   reference.

:p8 bouncer:  A glider {reflector} constructed by Noam Elkies in
   September 1998, with a minimum {repeat time} of 24 ticks.  It is a
   {constellation} containing a {figure-8}, {boat}, {eater1}, and
   {block}.  For {colour-preserving} glider reflectors see {p8 bumper}
   and the {stable} {Snark} reflector.
	................*.
	...............*..
	...............***
	..................
	..................
	..................
	..........*.......
	.........*........
	.........***......
	..................
	.............**...
	.........**..**...
	........*.*.......
	.........*........
	.....*............
	....*.*....**.....
	...*...*...*......
	..*...*.....***...
	.*...*........*...
	*...*.............
	.*.*..............
	..*...............

:p8 bumper:  A periodic {colour-preserving} {glider} {reflector} with a
   {blocker} attached to provide the necessary spark.  The minimum
   {repeat time} is 40 ticks.  For an equivalent {colour-changing}
   periodic glider reflector see {p8 bouncer}.  A {stable} {Snark}
   reflector can be substituted for any {bumper}.  This changes the
   timing of the output glider, which can be useful for rephasing
   periodic glider streams.
	....................*..
	....................*.*
	....................**.
	.......................
	.......................
	.......................
	.......................
	.......................
	.......................
	.......................
	..........*............
	..........*.*..........
	..........**...........
	.......................
	........**.............
	.**....*..*............
	.**.....*.*............
	.**......*.............
	..*....................
	.*.*.........**........
	**.*.........*.........
	..............***......
	................*......
	.**....................
	.**....................

:p8 G-to-H:  A small periodic variant of a stable two-glider-to-Herschel
   component found by Paul Callahan in November 1998  and used in the
   {Callahan G-to-H}, {Silver reflector} and {Silver G-to-H}.  The
   minimum {repeat time} is 192 ticks, though some lower periods such as
   96 are possible via {overclocking}.  Here a {ghost Herschel} marks
   the output signal location:
	....*.........*...................
	....***.....***...................
	.......*...*......................
	..*...**...**.....................
	...*..............................
	.***..............................
	..................................
	..................................
	..................................
	...............................*..
	...............................*..
	....................**.........***
	....................**...........*
	........**........................
	.......*..*.......................
	..**....**........................
	.*.*..............................
	.*................................
	**................................
	..........**......................
	..........*.......................
	...........***....................
	.............*...........**.......
	.....................**..**.......
	....................*.*...........
	.....................*............
	.................*................
	................*.*....**.........
	...............*...*...*..........
	..............*...*.....***.......
	.............*...*........*.......
	............*...*.................
	.............*.*..................
	..............*...................

:p8 reflector:  Traditional name for {p8 bouncer} before 2016, but with
   the discovery of the {p8 bumper} this has become an ambiguous
   reference.

:p90 gun:  A glider gun with {true} period 90.  The one below by Dean
   Hickerson uses the output of two p30 guns in a period-multiplying
   reaction:
	......................................*.........................
	......................................****......................
	................................**.....****.......*.............
	...........................*...*..*....*..*......*.*............
	..........................*.*...**.....****....**...*...........
	.........**...............**.*........****.....**...*.........**
	.........*.*..............**.**.......*........**...*.........**
	....**......*.............**.*...................*.*............
	**.*..*..*..*.............*.*.....................*.............
	**..**......*........*.....*...........*.*......................
	.........*.*.......*.*.................**.......................
	.........**.........**..................*.......................
	................................................................
	................................................................
	...........................................**...................
	...........................................**...................
	................................................................
	................................................................
	................................................................
	................................................................
	................................................................
	................................................................
	........................................**......................
	........................................*.......................
	.........................................***....................
	...........................................*....................

:p92 gun:  A glider gun with a {true} period of 92.  The first one was
   found by Bill Gosper in 1971 using a period doubling reaction using
   two p46 guns.  Many different p92 guns are known that use multiple
   {twin bees shuttle}s.  A period 92 gun can also be made by adding a
   {semi-cenark} to any period 46 glider gun.
     On 18 November 2017, Martin Grant found a new gun using one twin
   bees shuttle and one {Tanner's p46} oscillator, making it the
   smallest known p92 gun.
	....**..............*.........................
	.....*.............*.*........................
	.....*.*...........*.*........................
	......**..**.....***.**....................**.
	..........**....*..........................**.
	.................***.**........*..............
	...................*.**....**..*..............
	.......**.*.*.............*.....*...........**
	.......**.*.*............**..*.*............**
	.......**...*.............**...*..............
	.......**....**......**....***................
	*......**.....**.....**.......................
	***.......***.*............***................
	...*.....**...*.*.*.......**...*..............
	..*.*......*..*...*......**..*.*............**
	..**.......*.*..*.*.......*.....*...........**
	...........................**..*..............
	..**...........................*..............
	..*........................................**.
	....*......................................**.
	...**.........................................
	........**....................................
	.........*.....................*..............
	......***.......................*.............
	......*.......................***.............

:p9 bumper:  A periodic {colour-preserving} {glider} {reflector} with a
   {repeat time} of 36.  Unlike the p5 through p8 cases where Noam
   Elkies' {domino} spark-based reflectors are available, no small
   period-9 {colour-changing} reflector is known.  A {stable} {Snark}
   reflector can be substituted for any {bumper}.  This changes the
   timing of the output glider, which can be useful for rephasing
   periodic glider streams.
	........................*..
	........................*.*
	........................**.
	...........................
	...........................
	...........................
	...........................
	...........................
	...........................
	...............*...........
	......**.......*.*.........
	.....*.*.......**..........
	.**..*.....................
	.*.*.**......**............
	...*...*....*..*...........
	*..*.*.**....*.*...........
	***..*.*......*............
	...**.*....................
	..*..*..*.........**.......
	...******.........*........
	...................***.....
	.....**..............*.....
	.....**....................

:pair of bookends:  = {bookends}

:pair of tables:  = {table on table}

:paperclip: (p1)  A relatively 180-degree rotationally {symmetric}
   14-{bit} {still life}.  The {Iwona} {methuselah} contains a paperclip
   in its {ash}.
	..**.
	.*..*
	.*.**
	**.*.
	*..*.
	.**..

:parallel grey ship:  = {with-the-grain grey ship}

:Parallel HBK: ((6,3)c/245912, p245912)  A much smaller successor to the
   {half-baked knightship}, constructed by Chris Cain in September 2014.
   Several slow-salvo recipes are needed to support the multi-glider
   salvo {seed}s at the upstream end of the spaceship.  "Parallel" means
   that these recipes are sent in parallel instead of one after the
   other, in series, as in the original HBK.

:Parallel HBK gun:  An {armless} constructor pattern that is programmed
   to build {Parallel HBK} oblique spaceships every 125906944 ticks.
   This gun was created by Chris Cain on 3 January 2015.

:parasite:  A self-sustaining reaction attached to the output of a rake
   or puffer, that damages or modifies the standard output.  Compare
   {tagalong}.  In 2009, while experimenting with {novelty generator}
   patterns in {Golly}, Mitchell Riley discovered parasites on glider
   streams from p20 and p8 backward rakes.  In some cases, parasites can
   even "reproduce", as in the pattern below, though the number of
   copies is limited since they will eventually use up their host glider
   stream:
	......*.............*.........
	.....***...........***........
	...**.***.........***.**......
	....*..*.**.....**.*..*.......
	.**.*....*.*...*.*....*.**....
	.**.*.*..*.**.**.*..*.*.**....
	.*........*.*.*.*........*....
	**.......**.*.*.**.......**...
	............*.*...............
	.......***.*...*.***..........
	......**...........**.........
	......*.....*....**..*........
	.....**....***...**..*........
	...........*.**...***.........
	............***....*..........
	............***...............
	............***...............
	............**................
	..............................
	...................*.*........
	....................**........
	...............**...*.........
	........**......**............
	.......**......*..............
	.........*....................
	..............................
	..............................
	.................**...........
	..........*......***..........
	.........***.*...***..........
	........**.*.....***..........
	........**......*.**..........
	........**......***....**.....
	........**.**....*.....*......
	.........**...........**......
	..........***.*...*.***.......
	...............*.*............
	...**.......**.*.*.**.......**
	....*........*.*.*.*........*.
	....**.*.*..*.**.**.*..*.*.**.
	....**.*....*.*...*.*....*.**.
	.......*..*.**.....**.*..*....
	......**.***.........***.**...
	........***...........***.....
	.........*.............*......

:parent:  A pattern is said to be a parent of the pattern it gives rise
   to after one generation.  Some patterns have infinitely many parents,
   but others have none at all (see {Garden of Eden}).  Typically
   parents are considered trivial if they contain groups of cells that
   can be removed without changing the result, such as isolated faraway
   cells.

:parent cells:  The three cells that cause a new cell to be born.

:parity:  Even or odd, particularly as applied to the {phase} of an
   oscillator or spaceship.  For example, in {slow salvo} constructions,
   the {intermediate target}s are frequently period 2, most often
   because they contain {blinker}s or {traffic light}s.  A glider
   striking a P2 constellation will generally produce a different result
   depending on its parity. Period-4 intermediate targets are rare (or
   not used), so it doesn't matter for example whether an odd-parity
   glider in a slow salvo is phase 1 or phase 3.  Only the even/odd
   parity is important.

:partial result:  An intermediate object found by a {search program}
   which might be a substantial part of a complete {spaceship} or
   {oscillator}, but which isn't complete.
     Running a partial result works for a few generations until the
   {speed of light} corruption from any unfinished edge destroys the
   whole object.  But a partial result can still be used to see whether
   the object (if ever finished) would provide a desired {spark} or
   {perturbation}.  If no partial results are found then it is likely
   that no such object exists under the constraints of the search.
     Very large partial results can indicate that there is a good chance
   that the object being searched for might actually exist (but this is
   no guarantee).  Rerunning the search using the partial result as a
   base and relaxing some constraints, widening or adjusting the search
   area, or splitting the object into multiple {arm}s might result in
   finding a complete working object.
     As an example, here is a large partial result for a period 6
   {knightship} found by Josh Ball in April 2017.  The first 22 columns
   were rediscovered in 2018 as part of the successful search for
   {Sir Robin}.  See also {almost knightship} for an earlier small
   example by Eugene Langvagen.
	....***...................
	...*..**..................
	...*....*.................
	..........................
	...***...**.***...........
	.**.*.*....*.**...........
	...*..*....*..**..........
	*..*........*.............
	*....*..**..*..*..........
	.*.***..**...**...........
	...**.*.**.*...*..........
	.........**.***...........
	.........*.....*..........
	............***..***......
	...............*.**.......
	..........**.*...***......
	..........**..*..**.......
	............****...*......
	.............**.*..*......
	...........**.*.*.*.......
	..............*...........
	...........*.......**.....
	............**.....**.....
	..............**.*........
	................***..*.*..
	................**...*....
	.................*........
	..................*****.*.
	...................**..***
	...................**....*
	.......................**.

:PD:  = {pentadecathlon}

:PD hassler:  = {p29 pentadecathlon hassler}

:PD-pair reflector:  A pair of {pentadecathlon}s arranged so that their
   {V spark}s turn a glider by 90 degrees.  The minimum {repeat time} is
   45 ticks.
	..............***......
	.......................
	.............*...*.....
	.............*...*.....
	.......................
	..............***......
	.......................
	.......................
	..............***......
	.......................
	.............*...*.....
	.............*...*.....
	....................*..
	..............***...*.*
	....................**.
	.......................
	*..*.**.*..*...........
	****.**.****...........
	*..*.**.*..*...........
   This was found by Mark Niemiec on 6 January 1996, which is relatively
   recent considering how old {pentadecathlon} {technology} is.

:pedestle: (p5)  An {oscillator} found by Dave Buckingham in 1973.
	.....*.....
	....*.*....
	.*..**.....
	.***.......
	.....***...
	...**...*..
	..*....*..*
	.*.*.*.*.**
	.*.*...*.*.
	**.*.*.*.*.
	*..*....*..
	..*...**...
	...***.....
	.......***.
	.....**..*.
	....*.*....
	.....*.....

:penny lane: (p4)  Found by Dave Buckingham, 1972.
	...**.....**...
	...*.......*...
	**.*.......*.**
	**.*.*****.*.**
	....*..*..*....
	.....*****.....
	...............
	.......*.......
	......*.*......
	.......*.......

:pentadecathlon: (p15)  Found in 1970 by Conway while tracking the
   history of short rows of cells, 10 cells giving this object, which is
   the most {natural} {oscillator} of period greater than 3.  In fact it
   is the fifth most common {oscillator} overall, appearing in random
   soups slightly more frequently than the {clock}, but much less
   frequently than the {blinker}, {toad}, {beacon} or {pulsar}.  The
   pentadecathlon can be constructed using just three gliders, as shown
   in {glider synthesis}.
	..*....*..
	**.****.**
	..*....*..
     The pentadecathlon is the only known oscillator that has two
   {phase}s that are different {polyomino}es.  It produces accessible
   {V spark}s and {domino} sparks, which give it a great capacity for
   doing {perturbation}s, especially for period 30 based {technology}.
   See {relay} for example.

:pentant: (p5)  Found by Dave Buckingham, July 1976.
	**........
	.*........
	.*.*......
	..**....**
	.........*
	.....****.
	.....*....
	..*...***.
	..****..*.
	.....*....
	....*.....
	....**....

:pentaplet:  Any 5-cell {polyplet}.

:pentapole: (p2)  The {barberpole} of length 5.
	**......
	*.*.....
	........
	..*.*...
	........
	....*.*.
	.......*
	......**

:pentoad: (p5)  Found by Bill Gosper, June 1977.  This is {extensible}:
   if an eater is moved back four spaces then another {Z-hexomino} can
   be inserted.  (This extensibility was discovered by Scott Kim.)
	...........**
	...........*.
	.........*.*.
	.........**..
	.....**......
	......*......
	......*......
	......**.....
	..**.........
	.*.*.........
	.*...........
	**...........

:pentomino:  Any 5-cell {polyomino}.  There are 12 such patterns, and
   Conway assigned them all letters in the range O to Z, loosely based
   on their shapes.  Only in the case of the {R-pentomino} has Conway's
   label remained in common use, but all of them can nonetheless be
   found in this lexicon.

:period:  The smallest number of generations it takes for an
   {oscillator} or {spaceship} to reappear in its original form.  The
   term can also be used for a {puffer}, {wick}, {fuse}, {superstring},
   stream of {spaceship}s, {factory} or {gun}.  In the last case there
   is a distinction between {true} period and {pseudo} period.  There is
   also a somewhat different concept of period for {wicktrailer}s.

:period doubler:  See {period multiplier}.

:periodic:  For {circuit} mechanisms, "periodic" is the opposite of {p1}
   or {stable}.  Periodic {circuit}s necessarily contain {oscillator}s,
   and therefore they can generally only accept input {signal}s that are
   {synchronized} to the combined {period} of those oscillators (but see
   {universal regulator}).
     For {signal} {stream}s, "periodic" means that signals will only be
   present in the stream at one out of every n ticks, where n is the
   {period} of the stream.  In a periodic {intermittent stream} there
   may be gaps, so that signals do not always appear at every nth tick.
   However, if a signal does appear, its distance measured in ticks from
   previous and future signals will always be an exact multiple of n.

:period multiplier:  A term commonly used for a {pulse divider}, because
   dividing the number of {signal}s in a regular stream by N necessarily
   multiplies the {period} by N.  The term "period multiplier" can be
   somewhat misleading in this context, because most such circuits can
   accept input streams that are not strictly {periodic}.
     Reactions have also been found to period double or period triple
   the output of some {rake}s to create high-period rakes in a
   relatively small space (i.e., an exponential increase in period for a
   linear increase in size).
     For {Herschel} signals and {glider gun}s, a number of small period
   doubler, tripler, and quadrupler mechanisms are known.  For example,
   the following {conduit} produces one output glider after accepting
   four input {B-heptomino}es, or four Herschels if a conduit such as
   {F117} is prepended that includes the same {BFx59H} converter.
	....................*........................
	....................***......................
	.......................*.....................
	............**........**.....................
	.............*...............................
	.............*.*.............................
	**............**.............................
	*.*..........................................
	..*..........................................
	..**.........................................
	.............................................
	.............................................
	...........................................**
	...........................................**
	.............................................
	.*...**......................................
	.**..**......................................
	..**.........................................
	.**..........................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.................................**..........
	.........**......................**..........
	........*.*..................................
	........*....................................
	.......**....................................
     See {semi-Snark} and {tremi-Snark} for additional examples using
   {glider} streams.  As of June 2018 no stable period-multiplying
   {elementary conduit}s are known for a multiplication factor of five
   or higher, though it is easy to construct composite ones.

:permanent switch:  A {signal}-carrying {circuit} that can be modified
   so that it cleanly absorbs any future signals instead of allowing
   them to pass.  Optionally there may be a separate mechanism to
   restore the circuit to its original function.
     In the following example, a glider from the northeast (shown) will
   perform a simple {block pull} that switches off an {F166} conduit, so
   that any future Herschel inputs will be cleanly absorbed.  A glider
   from the southwest (also shown) can restore the block to its original
   position.
	.**........................................................
	..*........................................................
	.*.........................................................
	.**...............................................**.......
	...................................................*.......
	..................................................*........
	..................................................**.......
	..................................*........................
	..................................*.*......................
	*...**............................**.......................
	**..**.....................................................
	.**......................**................................
	**.......................**..........................**....
	.....................................................**....
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	.............**............................................
	............*.*........**..................................
	..............*.......*.*..................................
	......................*....................................
	.....................**.........................**.........
	................................................**.........
	...........................................................
	...........................................................
	..................................**.....................**
	...................................*......................*
	................................***....................***.
	................................*......................*...
	............................................**.............
	............................................*..............
	.............................................***...........
	...............................................*...........

:perpendicular grey ship:  = {against-the-grain grey ship}

:perturb:  To change the fate of an object by reacting it with other
   objects.  Typically, the other objects are sparks from {spaceship}s
   or {oscillator}s, or are {eater}s or impacting spaceships.
   Perturbations are typically done to turn a {dirty} reaction into a
   {clean} one, or to change the products of a reaction. In many
   desirable cases the perturbing objects are not destroyed by the
   reaction, or else are easily replenished.

:perturbation:  = {perturb}.

:PF35W:  One of the three {elementary} conduits used in the composite
   {Fx176} {Herschel conduit}.  It converts an input {pi-heptomino} into
   an output {wing} in 35 ticks.  In November 2017, Aidan F. Pierce
   discovered the compact PF35W variant below, which improved the repeat
   time of the Fx176 to 73 ticks and allowed {glider}s from following
   {dependent conduit}s to escape freely:
	*.........**...
	***....**..*...
	...*..*..**....
	..**...**..***.
	.........*.*..*
	.........*...**
	..........*....
	.........**....
	...............
	...............
	...............
	...............
	...***.........
	.....*.........
	...***.........
	...............
	...............
	...............
	...............
	...............
	...............
	...............
	...............
	..**...........
	...*...........
	***............
	*..............
   Several variants of the key catalyst are known, including {weld}ed
   additions for the Fx176 that absorb the following Herschel's first
   natural glider, since a standard fishhook eater doesn't quite fit.
   The following is a complete {Fx176} conduit incorporating the new
   PF45W:
	   ......................*...........................
	......................***...**....................
	..............**.........*..*..**.................
	..............**........**...**..*................
	...............................*.***..............
	...............................*....*.**..........
	................................*.*.*.*.*.........
	...............................**.**...*..........
	**................................................
	.*...................................*****........
	.*.*.................................*...*........
	..**...................................*..........
	.........................***..........***.........
	...........................*.............*........
	.........................***............**........
	..................................................
	..................................................
	..................................................
	..*...............................................
	..*.*...............................**...........*
	..***...............................**.........***
	....*..........................................*..
	...............................................*..
	..............**........**........................
	..............**..**.....*........................
	..................*.*.***.........................
	....................*.*...........................
	....................**....**......................
	.........................*.*....**................
	.........................*......**................
	........................**........................

:phase:  A representative generation of a periodic object such as an
   {oscillator} or {spaceship}.  The number of phases is equal to the
   {period} of the object.  The phases of an object usually repeat in
   the same cyclic sequence forever, although some {perturbation}s can
   cause a {phase change}.

:phase change:  A {perturbation} of a periodic object that causes the
   object to skip forward or backward by one or more {phase}s.  If the
   perturbation is repeated indefinitely, this can effectively change
   the {period} of the object.  An example of this, found by Dean
   Hickerson in November 1998, is shown below.  In this example, the
   period of the {oscillator} would be 7 if the {mold} were removed, but
   the period is increased to 8 because of the repeated phase changes
   caused by the mold's {spark}.
	..........*....
	.........*.**..
	..**.........*.
	..*......*..*.*
	.......*...*..*
	******.*....**.
	*..............
	.**.**...**....
	..*.*....*.*...
	..*.*......*...
	...*.......**..
     The following pattern demonstrates a p4 c/2 {spaceship} found by
   Jason Summers, in which the phase is changed as it deletes a
   {forward glider}.  This phase change allows the spaceship to be used
   to delete a glider wave produced by a {rake} whose period is 2 (mod
   4).
	........*...........................
	.......***.**.......................
	......**...*.**.....................
	.....**..*.....*....................
	......*.....*...*.***...............
	.....**.....*...*.*..*..............
	...**.*.**....*.*.*...*.............
	....*.*..**...........*.............
	.**.*..*..*.........*...............
	.**.*.....**.........*.***..........
	.*.*.............***.*.*.**.........
	**.**...........**.*..*.*.*.........
	..............**.*...***..**.....**.
	.............*...*......*........*.*
	............*.....*..**.*.**.....*..
	...........*..*.*......*.*..........
	...........*.....**....***..........
	.............*..........*...........
	..........*.*...........*...........
	.........**.*.***...................
	........*.*.*...*...................
	.......**.*.........................
	......*...*.....**..................
	....................................
	......**.**.........................
     Phase changing reactions have enabled the construction of
   spaceships having periods that were otherwise unknown, and also allow
   the construction of period-doubling and period-tripling {convoy}s to
   easily produce very high period rakes.
     See also {blinker puffer}.

:phase shift:  = {phase change}

:phi:  The following common {spark}.  The name comes from the shape in
   the generation after the one shown here.
	.***.
	*...*
	*...*
	.***.
   One {oscillator} which produces this spark is {Tanner's p46}.  The
   {pentadecathlon} produces a slightly corrupted version of this spark.

:phi calculator: (p1 circuitry)  See {pi calculator}.

:phoenix:  Any pattern all of whose cells die in every generation, but
   which never dies as a whole.  A {spaceship} cannot be a phoenix, and
   in fact every finite phoenix eventually evolves into an {oscillator}.
   The following 12-cell oscillator (found by the MIT group in December
   1971) is the smallest known phoenix, and is sometimes called simply
   "the phoenix".
	....*...
	..*.*...
	......*.
	**......
	......**
	.*......
	...*.*..
	...*....
   This is {extensible} and is just the first of a family of phoenixes
   made by joining {component}s together to form a loop.  Here is
   another member of this family.
	.....................*.......*......
	.....................*.*.....*.*....
	.................*.*.....*.*........
	.................*.......*......**..
	.....*.......*.*....................
	.....*.*.....*...................*..
	...*.....*.*........................
	.........*........................**
	..**................................
	..................................*.
	.*..................................
	................................**..
	**........................*.........
	........................*.*.....*...
	..*...................*.....*.*.....
	....................*.*.......*.....
	..**......*.......*.................
	........*.*.....*.*.................
	....*.*.....*.*.....................
	......*.......*.....................
   Every known phoenix oscillator has period 2.  In January 2000,
   Stephen Silver showed that a period 3 oscillator cannot be a phoenix.
   The situation for higher periods is unknown.
     An easy {synthesis} of the phoenix is possible using four blocks as
   {seed}s.  A {puffer} creating a growing row of phoenixes has the
   unusual property that the percentage of live cells that stay alive
   for more than one generation approaches zero.  See {lone dot agar}
   for an example of an infinite phoenix.

:pi:  = {pi-heptomino}

:Pianola breeder:  A series of patterns by Paul Tooke in 2010, based on
   a simplification and extension of the {Gemini} spaceship's
   construction mechanism.  Tooke  produced a number of
   slow-salvo-constructed patterns with {superlinear growth}, including
   a series of breeder patterns of previously unknown types.  For some
   patterns, the Gemini's two {construction arm}s were moved to a
   permanent stationary platform, using fourteen glider-loop channels
   instead of twelve.
     Some of these breeder patterns remain difficult to classify
   unambiguously.  For example, one pattern was designed to be an MSS
   breeder - a modified {Gemini} spaceship puffing {slide gun}s which
   build lines of {block}s.  However, the slide guns produce both moving
   and stationary objects at a linear rate, because streams of gliders
   are needed to reach out to the construction zone to do the {push}
   reaction and build more blocks.  The pattern could therefore be
   classified as a hybrid MSM/MSS breeder.  Other breeder patterns
   utilizing slide guns and {universal constructor} technology are
   likely to cause similar classification ambiguities.

:pi calculator: (p1 circuitry)  A device constructed by Adam P. Goucher
   in February 2010, which calculates the decimal digits of pi (the
   transcendental number, not the Life pattern!) and displays them in
   the Life universe as 8x10 dot matrix characters formed by
   arrangements of blocks along a diagonal stripe at the top.  A {push}
   reaction moves a ten-block diagonal cursor to the next position as
   part of the "printing" operation for each new digit.
     The actual calculation is done in binary, using a streaming spigot
   algorithm based on linear fractional transformations.  The pi
   calculator is made up of a 188-state computer connected to a printing
   device via period-8 {regulator}s and a binary-to-decimal conversion
   mechanism.  The complete pattern can be found in {Golly}'s Very Large
   Patterns online archive, along with the very similar 177-state phi
   calculator which uses a simpler algorithm to calculate and print the
   Golden Ratio.

:pi climber:  The reaction that defines rate of travel of the
   {Caterpillar} spaceship.  A pi climber consists of a pi-heptomino
   "climbing" a chain of blinkers, moving 17 cells every 45 ticks, and
   leaving behind an identical chain of blinkers, shifted downward by 6
   cells.  A single pi climber does not produce any gliders or other
   output, but two or more of them travelling on nearby blinker chains
   can be arranged to emit gliders every 45 ticks.  Compare
   {Herschel-pair climber}.
	..*..
	..*..
	..*..
	.....
	.....
	.....
	.....
	.....
	.....
	.....
	.....
	.....
	.....
	.....
	.....
	..*..
	.***.
	.*.*.

:pi-heptomino: (stabilizes at time 173)  A common pattern.  The name is
   also applied to later generations of this object.  In a {pi ship},
   for example, the pi-heptomino itself never arises.
	***
	*.*
	*.*

:pincers:  = {great on-off}

:pinwheel: (p4)  Found by Simon Norton, April 1970.  Compare {clock II}.
	......**....
	......**....
	............
	....****....
	**.*....*...
	**.*..*.*...
	...*...**.**
	...*.*..*.**
	....****....
	............
	....**......
	....**......

:pi orbital: (p168)  Found by Noam Elkies, August 1995.  In this
   {oscillator}, a {pi-heptomino} is turned ninety degrees every 42
   generations.  A second pi can be inserted to reduce the period to 84.
	..............**....**....**...............................
	.............*..*.*....*.*..*..............................
	.............***..........***..............................
	................**......**.................................
	...............*..******..*................................
	...............**........**................................
	...........................................................
	........*.............................**..........*........
	.......*...***......*.........*.......**.........*.*.......
	........*.*****..........***...*...........................
	............*...*.....*.*****.*..................*.........
	............**....***.....*......................**........
	............**....***....**...................*****........
	...................*.....**...................**.**.....**.
	.................................................*......*.*
	.....................................................**.*.*
	.....................................................*.*.*.
	.......................................................*...
	...................................***.........*.*...*..*..
	.......**..........................*..*........*..*.....*..
	.......**..............................*.......*.*..*...*..
	...................................*..*.............*...*..
	...................................***..................*..
	.....................................................*..*..
	................................................*......*...
	.............................................**.**...*.*.*.
	.............................................*****...**.*.*
	.........*......................................**......*.*
	........*.*.....................................*.......**.
	...........................................................
	.**.......*.....................................*.*........
	*.*......**......................................*.........
	*.*.**...*****.............................................
	.*.*.*...**.**.............................................
	...*......*................................................
	..*..*.....................................................
	..*........................................................
	..*...*....................................................
	..*...*..*.*......................................**.......
	..*.....*..*......................................**.......
	..*..*...*.*...............................................
	...*.......................................................
	.*.*.*.....................................................
	*.*.**.....................................................
	*.*......*.................................................
	.**.....**.**...................**.....*...................
	........*****...................**....***....**............
	........**......................*.....***....**............
	.........*..................*.*****.*.....*...*............
	...........................*...***..........*****.*........
	.......*.*.........**.......*.........*......***...*.......
	........*..........**.............................*........
	...........................................................
	................................**........**...............
	................................*..******..*...............
	.................................**......**................
	..............................***..........***.............
	..............................*..*.*....*.*..*.............
	...............................**....**....**..............

:pi portraitor: (p32)  Found by Robert Wainwright in 1984 or 1985.
   Compare with {gourmet} and {popover}.
	...........**...........
	......**.*....*.**......
	......*..........*......
	.......**......**.......
	....***..******..***....
	....*..*........*..*....
	.**.*.*..........*.*.**.
	.*.*.*............*.*.*.
	...*................*...
	.*..*..............*..*.
	....*.......***....*....
	*...*.......*.*....*...*
	*...*.......*.*....*...*
	....*..............*....
	.*..*..............*..*.
	...*................*...
	.*.*.*............*.*.*.
	.**.*.*..........*.*.**.
	....*..*........*..*....
	....***..******..***....
	.......**......**.......
	......*..........*......
	......**.*....*.**......
	...........**...........

:pipsquirt:  = {pipsquirter}

:pipsquirter:  An {oscillator} that produces a {domino} {spark} that is
   orientated parallel to the direction from which it is produced (in
   contrast to domino sparkers like the {pentadecathlon} and {HWSS},
   which produce domino sparks perpendicular to the direction of
   production).  See {p6 pipsquirter}, {p7 pipsquirter}.

:pi ship:  A {growing spaceship} in which the back part consists of a
   {pi-heptomino} travelling at a speed of 3c/10.  The first example was
   constructed by David Bell.  All known pi ships are too large to show
   here, but the following diagram shows how the pi fuse works.
	............*............
	...........*.*...........
	**........**.**........**
	**.....................**

:piston: (p2)  Found in 1971.
	**.......**
	*.*..*..*.*
	..****..*..
	*.*..*..*.*
	**.......**

:pi wave:  A line of {pi-heptomino}es stabilizing one another.  For
   example, an infinite line of pi-heptominoes arranged as shown below
   produces a pi wave that moves at a speed of 3c/10 with period 30, and
   leaves no debris.
	***...............***...............***...............***
	*.*...............*.*...............*.*...............*.*
	*.*...............*.*...............*.*...............*.*

:pixel:  = {cell}

:plet:  = {polyplet}

:polyomino:  A finite collection of orthogonally connected cells.  The
   mathematical study of polyominoes was initiated by Solomon Golomb in
   1953.  Conway's early investigations of Life and other cellular
   automata involved tracking the histories of small polyominoes, this
   being a reasonable way to ascertain the typical behaviour of
   different cellular automata when the patterns had to be evolved by
   hand rather than by computer.  Polyominoes have no special
   significance in Life, but their extensive study during the early
   years lead to a number of important discoveries and has influenced
   the terminology of Life.  (Note on spelling:  As with "dominoes" the
   plural may also be spelt without an e.  In this lexicon I have
   followed Golomb in using the longer form.)
     It is possible for a polyomino to be an {oscillator}.  In fact
   there are infinitely many examples of such polyominoes, namely the
   {cross} and its larger analogues.  The only other known examples are
   the {block}, the {blinker}, the {toad}, the {star} and (in two
   different phases) the {pentadecathlon}.
     A polyomino can also be a {spaceship}, as the {LWSS}, {MWSS} and
   {HWSS} show.

:polyplet:  A finite collection of orthogonally or diagonally connected
   cells.  This king-wise connectivity is a more natural concept in Life
   than the orthogonal connectivity of the {polyomino}.

:pond: (p1)
	.**.
	*..*
	*..*
	.**.

:pond on pond: (p1)  This term is often used to mean {bi-pond}, but may
   also be used of the following {pseudo still life}.
	.**...**.
	*..*.*..*
	*..*.*..*
	.**...**.

:popover: (p32)  Found by Robert Wainwright in August 1984.  Compare
   with {gourmet} and {pi portraitor}.
	.....................*..........
	.....................*..........
	.....................***........
	.............**.......**........
	.............**..***..**........
	...................***..........
	...................***..........
	..............**................
	..***........*..*...............
	..***........*.*................
	***..**...*...*....***..........
	.....**...*.....................
	....***...*.....................
	....*.................**...**...
	....*...........***..*..*..**...
	........*.......*.*...*.*.......
	.......*.*......*.*....*........
	...**..*..*................*....
	...**...**.................*....
	.....................*...***....
	.....................*...**.....
	..........***........*...**..***
	.................**........***..
	................*..*.......***..
	................*.*.............
	..........***....*..............
	..........***...................
	........**..***..**.............
	........**.......**.............
	........***.....................
	..........*.....................
	..........*.....................

:population:  The number of ON cells.

:P-pentomino:  Conway's name for the following {pentomino}, a common
   {spark}.
	**
	**
	*.

:PPS: (c/5 orthogonally, p30)  A pre-pulsar spaceship.  Any of three
   different p30 c/5 orthogonal {spaceship}s in which a {pre-pulsar} is
   pushed by a pair of {spider}s.  The back sparks of the spaceship can
   be used to perturb gliders in many different ways, allowing the easy
   construction of c/5 puffers.  The first PPS was found by David Bell
   in May 1998 based on a p15 pre-pulsar spaceship found by Noam Elkies
   in December 1997.  See also {SPPS} and {APPS}.
     The pattern below shows the basic mechanism of a PPS.  The two
   isolated sparks at the left and right sides are the {edge spark}s
   from the two supporting spiders.
	...*.....*...
	..*.*...*.*..
	.............
	..***...***..
	.............
	.............
	.............
	..***...***..
	.............
	*.*.*...*.*.*
	...*.....*...

:pre-beehive:  The following common {parent} of the {beehive}.
	***
	***

:pre-block:  The following common {parent} of the {block}.  Another such
   pattern is the {grin}.
	*.
	**

:precursor:  = {predecessor}

:predecessor:  Any pattern that evolves into a given pattern after one
   or more generations.

:pre-pre-block:  A common predecessor to the {pre-block} (and thus the
   {block}):
	*.*
	.**
   This is easily created by a two-glider collision.  Hitting the
   pre-pre-block with a glider can create a {MWSS}.  Both of these
   reactions are shown below:
	.*..........
	..*.........
	***.........
	............
	............
	...***....**
	.....*...**.
	....*......*

:pre-pulsar:  A common {predecessor} of the {pulsar}, such as that shown
   below.  This duplicates itself in 15 generations.  (It fails,
   however, to be a true {replicator} because of the way the two copies
   then interact.)
	***...***
	*.*...*.*
	***...***
     A pair of {tub}s can be placed to eat half the pre-pulsar as it
   replicates; this gives the p30 oscillator {Eureka} where the
   pre-pulsar's replication becomes a movement back and forth. See
   {twirling T-tetsons II} for a variation on this idea.  By other means
   the replication of the pre-pulsar can be made to occur in just 14
   generations as half of it is eaten; this allows the construction of
   p28 and p29 oscillators.  The pre-pulsar was also a vital component
   of the first known p26 and p47 oscillators.
     See also {PPS}.

:pre-pulsar spaceship:  = {PPS}.

:pressure cooker: (p3)  Found by the MIT group in September 1971.
   Compare {mini pressure cooker}.
	.....*.....
	....*.*....
	....*.*....
	...**.**...
	*.*.....*.*
	**.*.*.*.**
	...*...*...
	...*...*...
	....***....
	...........
	...*.**....
	...**.*....

:primer:  A pattern originally constructed by Dean Hickerson in November
   1991 that emits a stream of {LWSS}s representing the prime numbers.
   Some improvements were found by Jason Summers in October 2005.

:PRNG:  = {pseudo-random number generator}

:propagator:  = {linear propagator}

:protein: (p3)  Found by Dave Buckingham, November 1972.
	....**.......
	....*........
	......*......
	..****.*.**..
	.*.....*.*..*
	.*..**.*.*.**
	**.*.....*...
	...*..**.*...
	...*....*....
	....****.....
	.............
	....**.......
	....**.......

:pseudo:  Opposite of {true}.  A {gun} emitting a period n {stream} of
   spaceships (or rakes) is said to be a pseudo period n gun if its
   mechanism oscillates with a period greater than n.  This period will
   necessarily be a multiple of n.  If the base mechanism's period is
   instead a fraction of n, then a {period multiplier} must also be
   present which is considered to be part of the mechanism, and the gun
   as a whole is still a true period gun.  For example, a {filter} may
   be used on a lower-period gun to produce a compound gun such as the
   true {p48 gun}.
     Pseudo period n glider guns are known to exist for all periods
   greater than or equal to 14, with smaller periods being impossible.
   All known {p14 gun}s are pseudo guns requiring several {signal}
   {inject}ions, so they are quite large.  The following smaller example
   is a pseudo period 123 gun, interleaving the streams from two true
   period 246 guns:
	..................................*...........................
	..................................***.........................
	................................**...*........................
	...............................*.*.**.*.......................
	..............................*..*..*.*.......................
	....................................*.**......................
	..................................*.*.........................
	......................***.......*.*.*.........................
	.................................**.**........................
	.....................*..*.....................................
	**...................***......................................
	.*............................................................
	.*.*...................**.**..................................
	..**...............**..**.*.*............**...................
	...................**..**...*............*....................
	...........................***.........*.*...........**.......
	.......................**..***.........**............*.*......
	..................*.*..***............................***.....
	..................*.*...**.............................**.....
	...................*.................................*.*......
	................................................**..*.*.......
	................................................*.*..*........
	.................................................****.........
	.............................**...................**..........
	.............................**...............................
	..............................................................
	..............................................................
	.....................................****.....................
	....................................*****.*...................
	.....................................*..*.*...................
	.....*...................................**...................
	....*.****.............................*.*....................
	...*.*.***..........................**............*.........**
	..*.*..............................*.****..........*........*.
	...*...............................*...**........***......*.*.
	...**.............**................**.*..................**..
	...**.............*.*................***......................
	...**..............***........................................
	....................**........................................
	..................*.*.........................................
	.............**..*.*..........................................
	.............*.*..*...........................................
	..............****..............................**............
	...............**...............................**............
	....................**.**.....................................
	.....................*.*......................................
	.....................*........................................
	..................**.*..*.....................................
	...................*.*.***....................................
	...................*.**...*...................................
	....................*...**....................................
	.....................***......................................
	.......................*......................................
     The same distinction between true and pseudo also exists for
   {puffer}s.

:pseudo-barberpole: (p5)  Found by Achim Flammenkamp in August 1994. In
   terms of its minimum {population} of 15 this is the smallest known p5
   {oscillator}.  See also {barberpole}.
	..........**
	...........*
	.........*..
	.......*.*..
	............
	.....*.*....
	............
	...*.*......
	............
	..**........
	*...........
	**..........

:pseudo-random glider generator:  A {pseudo-random number generator} in
   which the bits are represented by the presence or absence of
   {glider}s.  The first pseudo-random glider generator was built by
   Bill Gosper.  David Bell built the first moving one in 1997, using
   c/3 {rake}s.

:pseudo-random number generator:  A pseudo-random number generator
   (PRNG) is an algorithm that produces a sequence of bits that looks
   random (but cannot really be random, being algorithmically
   determined).
     In Life, the term refers to a PRNG implemented as a Life pattern,
   with the bits represented by the presence or absence of objects such
   as {glider}s or {block}s.  Such a PRNG usually contains gliders or
   other {spaceship}s in a loop with a feedback mechanism that causes
   later spaceships to interfere with the generation of earlier
   spaceships.  The {period} can be very high, as a loop of n spaceships
   has 2^n possible states.

:pseudo still life:  A {stable} pattern whose live cells are either
   immediately adjacent to each other, or are connected into a single
   group by adjacent dead cells where birth is suppressed by
   overpopulation.
     The definition of {strict still life} rules out such stable
   patterns as the {bi-block}.  In such patterns there are dead cells
   which have more than 3 neighbours in total, but fewer than 3 in any
   component still life.  These patterns are called pseudo still lifes,
   and have been enumerated up to 32 bits, as shown in the table below.
	--------------
	Bits    Number
	--------------
	 8           1
	 9           1
	10           7
	11          16
	12          55
	13         110
	14         279
	15         620
	16        1645
	17        4067
	18       10843
	19       27250
	20       70637
	21      179011
	22      462086
	23     1184882
	24     3068984
	25     7906676
	26    20463274
	27    52816265
	28   136655095
	29   353198379
	30   914075620
	31  2364815358
	32  6123084116
	--------------
     Attribution of these counts is given in {strict still life}; see
   also {https://oeis.org/A056613}.  The unique 32-bit {triple pseudo}
   still life is included in the last count in the table.  As the number
   of bits increases, the pseudo still life count goes up exponentially
   by approximately O(2.56^n).  By comparison, the rate for
   {strict still life}s is about O(2.46^n) while for {quasi still life}s
   it's around O(3.04^n).
     If a stable pattern's live cells plus its overpopulated dead cells
   do not form a single mutually adjacent group, the pattern is usually
   referred to as a {constellation}.  It is also a {still life} in the
   general sense, but is neither "pseudo" nor "strict".

:puffer:  An object that moves like a {spaceship}, except that it leaves
   debris behind.  The first known puffers were found by Bill Gosper and
   travelled at c/2 orthogonally (see diagram below for the very first
   one, found in 1971).
	.***......*.....*......***.
	*..*.....***...***.....*..*
	...*....**.*...*.**....*...
	...*...................*...
	...*..*.............*..*...
	...*..**...........**..*...
	..*...**...........**...*..
     Not long afterwards c/12 diagonal puffers were found (see
   {switch engine}).  Discounting {wickstretcher}s, which are not
   puffers in the conventional sense, no new velocity was obtained after
   this until David Bell found the first c/3 orthogonal puffer in April
   1996.  Other new puffer speeds followed over the next several years.
     Many spaceships that travel orthogonally at a speed less than c/2
   have useful side or back {spark}s.  These can be used to perturb
   {standard spaceship}s that approach from behind.  A common technique
   for creating puffers for a new speed uses a {convoy} of the new
   spaceships to create debris from an approaching standard spaceship
   such that a new standard spaceship is recreated on the same path as
   the original one.  This forms a closed loop, resulting in a
   high-period puffer for the new speed.
     As of June 2018, puffers have been found matching every known
   velocity of {elementary} spaceship, except for c/6 and c/7 diagonal
   and (2,1)c/6.  It is also generally easy to create puffers based on
   {macro-spaceship}s, simply by removing some part of the trailing
   cleanup mechanism.

:puffer engine:  A pattern which can be used as the main component of a
   {puffer}.  The pattern may itself be a puffer (e.g. the classic
   {puffer train}), it may be a spaceship (e.g. the {Schick engine}), or
   it may even be unstable (e.g. the {switch engine}).

:pufferfish: (c/2, p12)  A puffer discovered by Richard Schank in
   November 2014, from a symmetric soup search using an early version of
   {apgsearch}.  It consists of a pair of {B-heptomino}es stabilised by
   a backend that leaves only pairs of blocks behind.  It is simple
   enough to be easily synthesized with gliders.
	...*.......*...
	..***.....***..
	.**..*...*..**.
	...***...***...
	...............
	....*.....*....
	..*..*...*..*..
	*.....*.*.....*
	**....*.*....**
	......*.*......
	...*.*...*.*...
	....*.....*....
   See {soup} for a random initial pattern, generated by {apgsearch} and
   recorded in {Catagolue}, that produces a pufferfish.

:pufferfish spaceship: (c/2, p36)  Generally, any {spaceship}
   constructed using {pufferfish}.  May refer specifically to the
   extensible c/2 {spaceship} constructed by Ivan Fomichev in December
   2014, the first such spaceship to contain no period-2 or period-4
   parts.  (The first two or three rows might be considered to be period
   2 or 4, but they are directly dependent on following rows for
   support.).
     The pattern consists of two adjacent {pufferfish} {puffer}s, plus
   four copies of a nontrivial period 36 c/2 {fuse} for pufferfish
   {exhaust}, discovered using a randomized soup search.
	.......*.......*..................*.......*........
	......***.....***................***.....***.......
	.....*..**...**..*..............**.*.....*.**......
	.....*...*...*...*...............**.*...*.**.......
	......**.**.**.**..............*.**.......**.*.....
	......**.*...*.**.............*.*..*.*.*.*..*.*....
	........*.....*...............*.*...**.**...*.*....
	.........**.**.................***.*.....*.***.....
	....**..*.....*..**.............***.......***......
	....**..*.....*..**.............**.........**......
	................................*...........*......
	........*.*.*.*................**...........**.....
	........**...**................**...........**.....
	...................................................
	...................................**...**.........
	...................*..........*....**...**.........
	...*..............***........***..............*....
	..***...**...*.*.**.*.......**.*.............***...
	.**..*..**.........*........***.............**.*...
	.****.*......*...*.*........***.............**.....
	**.....*.......**..**.......****..............**...
	.*................*..*......*..*...........*..**...
	.*.***..*....*.*..**.......**..............*....*..
	.*.*...**....*.*..**...*....*.*...........*..*.*...
	.**......*..*.......*..*....***..........**...**...
	*.....*.*....*.*....*.**................*..........
	.**..*..*....*......*.**............*....**........
	.**...**.......**...**.**..**......******..........
	........................*....*....*.*.*.*.......***
	..............................*...*..*.........*...
	..............................*....*..........*....
	.............................*.................*.*.

:puffer train:  The full name for a {puffer}, coined by Conway before
   any examples were known.  The term was also applied specifically to
   the classic puffer train found by Bill Gosper and shown below. This
   is very {dirty}, and the tail does not stabilize until generation
   5533.  It consists of a {B-heptomino} (shown here one generation
   before the standard form) escorted by two {LWSS}.  (This was the
   second known puffer.  The first is shown under {puffer}.)
	.***...........***
	*..*..........*..*
	...*....***......*
	...*....*..*.....*
	..*....*........*.
   In April 2006, Jason Summers found a way to make the classic puffer
   train into a p20 {spaceship} by adding a {glider} at the back:
	***...........***.
	*..*..........*..*
	*......***....*...
	*.....*..*....*...
	.*.*..*...*....*.*
	.......****.......
	.........*........
	..................
	..................
	..................
	.......***........
	.......*..........
	........*.........

:puff suppressor:  An attachment at the back of a {line puffer} that
   suppresses all or some of its puffing action.  The example below (by
   Hartmut Holzwart) has a 3-cell puff suppressor at the back which
   suppresses the entire puff, making a p2 {spaceship}.  If you delete
   this puff suppressor then you get a p60 double {beehive} {puffer}.
   Puff suppressors were first recognised by Alan Hensel in April 1994.
	............*....................
	..........**.*...................
	..........**...*.................
	........*...**.*.....*...........
	........****.**...****.......*.*.
	......*......*....***.....*.*..*.
	......*******...*...*....*..*....
	...*.*......**..*...*.*.**....*..
	..*********.....*..**........*...
	.**..............*.**.****...*..*
	**....**.*..........*...*..*.*...
	.**....*........***......*.*.*..*
	.........*......**......*....**..
	.**....*........***......*.*.*..*
	**....**.*..........*...*..*.*...
	.**..............*.**.****...*..*
	..*********.....*..**........*...
	...*.*......**..*...*.*.**....*..
	......*******...*...*....*..*....
	......*......*....***.....*.*..*.
	........****.**...****.......*.*.
	........*...**.*.....*...........
	..........**...*.................
	..........**.*...................
	............*....................

:pull:  A reaction, most often mediated by gliders, that moves an object
   closer to the source of the reaction.  See {block pull},
   {blinker pull}, {loaf pull}; also {elbow}.

:pulsar: (p3)  Despite its size, this is the fourth most common
   {oscillator} (and by far the most common of period greater than 2)
   and was found very early on by Conway.  See also {pre-pulsar},
   {pulsar quadrant}, and {quasar}.
	..***...***..
	.............
	*....*.*....*
	*....*.*....*
	*....*.*....*
	..***...***..
	.............
	..***...***..
	*....*.*....*
	*....*.*....*
	*....*.*....*
	.............
	..***...***..

:pulsar 18-22-20:  = {two pulsar quadrants}

:pulsar CP 48-56-72:  = {pulsar}  (The numbers refer to the populations
   of the three {phase}s.)

:Pulsar Pixel Display: (p30 circuitry)  A large-scale raster line
   display device constructed by Mark Walsh in August 2010, where
   {pulsar}s form the individual pixels in an otherwise empty grid.  The
   published sample pattern displays and erases eight 7x5-pixel
   characters on each of two lines of text.

:pulsar quadrant: (p3)  This consists of a quarter of the outer part of
   a {pulsar} stabilized by a {cis fuse with two tails}.  This is
   reminiscent of {mold} and {jam}.  Found by Dave Buckingham in July
   1973.  See also {two pulsar quadrants}.
	.....*..
	...***..
	..*...**
	*..*..*.
	*...*.*.
	*....*..
	........
	..***...

:pulse:  A moving object, such as a {spaceship} or {Herschel}, which can
   be used to transmit information.  See {pulse divider}.
     Also another name for a {pulsar quadrant}.

:pulse divider:  A mechanism that lets every n-th object that reaches it
   pass through, and deletes all the rest, where n > 1 and the objects
   are typically {glider}s, {spaceship}s or {Herschel}s.  A common
   synonym is {period multiplier}.  For n=2, the simplest known stable
   pulse dividers are the {semi-Snark}s.
     The following diagram shows a p5 glider pulse divider by Dieter
   Leithner (February 1998).  The first glider moves the centre block
   and is reflected at 90 degrees.  The next glider to come along will
   not be reflected, but will move the block back to its original
   position.  The relatively small size and low period of this example
   made it useful for constructing compact glider {gun}s of certain
   periods, but it became largely obsolete with the discovery of the
   {stable} {CC semi-Snark}, which uses the same basic mechanism.
   Period 7, 22, 36 and 46 versions of this pulse divider are also
   known.
	.....**...................
	.....**...................
	..........................
	..................**......
	.................*..*.....
	.................*.*..*..*
	*...............**.*.*****
	.**...........*...**......
	**...............**..***..
	.............*...*.*..*.*.
	........**.......**..**.*.
	........**....*...**...*..
	................**.*.**...
	.................*.*.*....
	.................*.*..*...
	..................*..**...
	..**......................
	...*......................
	***.......................
	*.........................
	..........................
	............**............
	............*.............
	.............***..........
	...............*..........

:pulshuttle V: (p30)  Found by Robert Wainwright, May 1985. Compare
   {Eureka}.
	.............*..............*.............
	............*.*.......*....*.*............
	.............*......**.**...*.............
	......................*...................
	..**......**..................**......**..
	*....*..*....*..............*....*..*....*
	*....*..*....*..............*....*..*....*
	*....*..*....*........*.....*....*..*....*
	..**......**........**.**.....**......**..
	......................*...................
	..........................................
	..........................................
	..**......**..................**......**..
	*....*..*....*........*.....*....*..*....*
	*....*..*....*......**.**...*....*..*....*
	*....*..*....*........*.....*....*..*....*
	..**......**..................**......**..
	..........................................
	..........................................
	......................*...................
	..**......**........**.**.....**......**..
	*....*..*....*........*.....*....*..*....*
	*....*..*....*..............*....*..*....*
	*....*..*....*..............*....*..*....*
	..**......**..................**......**..
	......................*...................
	.............*......**.**...*.............
	............*.*.......*....*.*............
	.............*..............*.............

:pure glider generator:  A pattern that evolves into one or more
   {glider}s, and nothing else.  There was some interest in these early
   on, but they are no longer considered important.  Here's a neat
   example:
	..*............
	..*............
	***............
	...............
	......***......
	.......*.......
	............***
	............*..
	............*..

:push:  A reaction that moves an object farther away from the source of
   the reaction.  See {sliding block memory}, {pi calculator}, {elbow},
   {universal constructor}.  See also {pull}, {fire}.

:pushalong:  Any {tagalong} at the front of a spaceship.  The following
   is an example found by David Bell in 1992, attached to the front of a
   {MWSS}.
	..***.*.....
	.****.*.....
	**..........
	.*.*........
	..****.*....
	...***......
	............
	............
	......*****.
	......*....*
	......*.....
	.......*...*
	.........*..

:pyrotechnecium: (p8)  Found by Dave Buckingham in 1972.
	.......*........
	.....*****......
	....*.....*.....
	.*..*.*.**.*....
	*.*.*.*....*..*.
	.*..*....*.*.*.*
	....*.**.*.*..*.
	.....*.....*....
	......*****.....
	........*.......

:pyrotechneczum:  A common mistaken spelling of {pyrotechnecium}, caused
   by a copying error in the early 1990s.

:python:  = {long snake}

:Q:  = {Quetzal}

:qd:  Abbreviation for {quarter diagonal}.

:Q-pentomino:  Conway's name for the following {pentomino}, a
   {traffic light} {predecessor}.
	****
	...*

:quad: (p2)  Found by Robert Kraus, April 1971.  Of all {oscillator}s
   that fit in a 6x6 box this is the only {flipper}.
	**..**
	*..*.*
	.*....
	....*.
	*.*..*
	**..**

:QuadLife:  A form of {colourised Life} in which there are four types of
   ON cell.  A newly-born cell takes the type of the majority of its
   three {parent cells}, or the remaining type if its parent cells are
   all of different types.  In areas where there are only two types of
   ON cell QuadLife reduces to {Immigration}.

:quadpole: (p2)  The {barberpole} of length 4.
	**.....
	*.*....
	.......
	..*.*..
	.......
	....*.*
	.....**

:quad pseudo:  A {still life} that can be broken down into four {stable}
   pieces but not into two or three.  This term may refer to the
   following 34-bit pattern, found by Gabriel Nivasch in July 2001, or
   any similar pattern with the same property.
	........**.
	...**.*..*.
	...*.**.*..
	........**.
	...*.**...*
	.***.**.**.
	*.......*..
	.***.**.*..
	...*.*.*...
     As a consequence of the Four-Colour Theorem, there can be no
   analogous objects requiring decomposition into five or more pieces.
   By convention, patterns like this and the {triple pseudo} are
   considered to be {pseudo still life}s, not {strict still life}s.  As
   of June 2018, it has been shown that no quad pseudo patterns exist
   with 32 or fewer bits, but a 33-bit pattern with this property may
   theoretically still be found.

:quadratic filter:  A {toolkit} developed by Dean Hickerson and Gabriel
   Nivasch in 2006, enabling the construction of patterns with
   asymptotic population growth matching an infinite number of different
   sublinear functions - namely, O(t^(1/2^n)) for any chosen n.  See
   also {exponential filter}, {recursive filter}.

:quadratic growth:  The fastest possible asymptotic rate of population
   growth for any Life pattern - O(t^2) in big-O notation, where t is
   the number of ticks.  The first quadratic-growth pattern found was
   Bill Gosper's 1971 {breeder}.  Many other types of breeders and
   {spacefiller}s have been constructed since.
     In April 2011, Stephen Silver gave an example of a one-cell-thick
   pattern over a million cells long that exhibited quadratic growth.
   In October 2015, Chris Cain constructed a one-cell-thick pattern with
   a reduced bounding box of 2596x1, improving on a series of previous
   longer results.  The smallest known quadratic growth pattern by
   initial population is the 23-cell {switch-engine ping-pong} by
   Michael Simkin.
     There are an infinite number of possible growth rates between
   linear and quadratic growth.  See {superlinear growth}.

:quadratic replicator:  A pattern that fills all or part of the Life
   plane by making copies of itself in a nonlinear way.  Small quadratic
   replicators are known in other Life-like rules, but as of July 2018
   no example has been found or constructed in Conway's Life.

:quadratic sawtooth:  Any {sawtooth} pattern with a quadratic envelope,
   or specifically a pattern assembled by Martin Grant in May 2015,
   consisting of two {caber tosser}s with period multipliers for timing
   which activate and deactivate two toggleable rake guns (see
   {toggleable gun}).  The gliders emitted by those rakes annihilate on
   the diagonal while the rakes are eaten by 2c/5 ships. All the rakes
   and gliders are destroyed before the next cycle.  See also
   {Osqrtlogt}.

:quadri-Snark:  A period-multiplying {colour-preserving} {signal}
   {conduit} found by Tanner Jacobi in October 2017, producing one
   output {glider} for every four input gliders.  It is made by
   replacing one of the eaters in a {tremi-Snark} with a {catalyst}
   found using {Bellman}.  The catalyst causes the formation of a {tub}
   which then requires an additional glider to delete.  However, this
   adds 5 ticks to the repeat time, so that it becomes 48.  If period
   quadrupling is needed with a {colour-changing} reaction, a
   {CP semi-Snark} and a {CC semi-Snark} can be used in series, or a
   period-multiplying {Herschel conduit} can be connected to a {syringe}
   and an appropriately chosen Herschel-to-glider {converter}.
	.*.......................................................
	..*......................................................
	***......................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.............*...........................................
	..............*..........................................
	............***..........................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	.........................*...............................
	..........................*..............................
	........................***..............**..............
	..........................................*..............
	........................................*.....**.........
	........................................**.....*.........
	...............................................*.**......
	........................................**..**.*..*......
	........................................**...*.**........
	.............................................*...........
	............................................**...........
	...................................................**....
	.....................................*.............*.*...
	......................................*..............*...
	....................................***..............*.**
	...........................................**.....**.*.*.
	...........................................**.....**.*.*.
	.....................................................*.**
	..................................**..............****..*
	.................................*.*..............*...**.
	.................................*..................**...
	................................**...................*...
	...................................................*.....
	...................................................**....

:quapole:  = {quadpole}

:quarter: (c/4 diagonally, p4)  The following {spaceship}, found by
   Jason Summers in September 2000.  The name is due to the 25-cell
   minimum population.  This is the smallest known {c/4 spaceship} other
   than the {glider}.  This spaceship can also be used to make the
   smallest known {tubstretcher}.
	........**...
	.......**....
	.........*...
	...........**
	..........*..
	.............
	.........*..*
	.**.....**...
	**.....*.....
	..*....*.*...
	....**..*....
	....**.......

:quarter diagonal:  A unit of measurement sometimes used for diagonal
   distances, especially for {slow salvo} glider {lane}s.  One advantage
   of measurement in quarter diagonals is that gliders travel diagonally
   at 1qd/tick, so that the same integer value can serve as either a
   time or a diagonal distance measurement.

:quasar: (p3)  Found by Robert Wainwright, August 1971.  This is related
   to the {pulsar}, and is just the smallest of an extensible series of
   p3 oscillators built using pulsar quadrants which are shifted with
   respect to each other.
	..........***...***..........
	.............................
	........*....*.*....*........
	........*....*.*....*........
	........*....*.*....*........
	..........***...***..........
	.............................
	........***.......***........
	..***..*....*...*....*..***..
	.......*....*...*....*.......
	*....*.*....*...*....*.*....*
	*....*.................*....*
	*....*..***.......***..*....*
	..***...................***..
	.............................
	..***...................***..
	*....*..***.......***..*....*
	*....*.................*....*
	*....*.*....*...*....*.*....*
	.......*....*...*....*.......
	..***..*....*...*....*..***..
	........***.......***........
	.............................
	..........***...***..........
	........*....*.*....*........
	........*....*.*....*........
	........*....*.*....*........
	.............................
	..........***...***..........
   Here is the next oscillator in the series.
	..................***...***..................
	.............................................
	................*....*.*....*................
	................*....*.*....*................
	................*....*.*....*................
	..................***...***..................
	.............................................
	................***.......***................
	..........***..*....*...*....*..***..........
	...............*....*...*....*...............
	........*....*.*....*...*....*.*....*........
	........*....*.................*....*........
	........*....*..***.......***..*....*........
	..........***...................***..........
	.............................................
	........***.......................***........
	..***..*....*...................*....*..***..
	.......*....*...................*....*.......
	*....*.*....*...................*....*.*....*
	*....*.................................*....*
	*....*..***.......................***..*....*
	..***...................................***..
	.............................................
	..***...................................***..
	*....*..***.......................***..*....*
	*....*.................................*....*
	*....*.*....*...................*....*.*....*
	.......*....*...................*....*.......
	..***..*....*...................*....*..***..
	........***.......................***........
	.............................................
	..........***...................***..........
	........*....*..***.......***..*....*........
	........*....*.................*....*........
	........*....*.*....*...*....*.*....*........
	...............*....*...*....*...............
	..........***..*....*...*....*..***..........
	................***.......***................
	.............................................
	..................***...***..................
	................*....*.*....*................
	................*....*.*....*................
	................*....*.*....*................
	.............................................
	..................***...***..................

:quasi still life:  A {stable} {constellation} where the individual
   {still life}s share dead cells, so the neighborhoods of those dead
   cells are changed, but all cells that used to remain dead from
   under-population still do so.  Under Life rules, this occurs when
   objects are diagonally adjacent (e.g., two {block}s sharing a single
   diagonal neighbor) or when single protruding cells in two objects
   such as {tub}s share multiple neighbors.  The term is due to Mark
   Niemiec.
	----------------
	Bits       Count
	----------------
	 8             6
	 9            13
	10            57
	11           141
	12           465
	13          1224
	14          3956
	15         11599
	16         36538
	17        107415
	18        327250
	19        972040
	20       2957488
	21       8879327
	22      26943317
	----------------
     As the number of bits increases, the quasi still life count goes up
   exponentially by approximately O(3.04^n), slightly more than a factor
   of three.  By comparison, the rate for {strict still life}s is about
   O(2.46^n) while for {pseudo still life}s it's around O(2.56^n).

:queen bee:  See {queen bee shuttle}.

:queen bee shuttle: (p30)  Found by Bill Gosper in 1970.  There are a
   number of ways to stabilize the ends.  Gosper originally stabilized
   shuttles against one another in a square of eight shuttles. Two
   simpler methods are shown here; for a third see {buckaroo}. The queen
   bee shuttle is the basis of all known {true} p30 {gun}s (see
   {Gosper glider gun}).
	.........*............
	.......*.*............
	......*.*.............
	**...*..*.............
	**....*.*.............
	.......*.*........**..
	.........*........*.*.
	....................*.
	....................**

:queen bee shuttle pair:  Any arrangement of two {queen bee shuttle}s
   such that the two {beehive}s created between them are consumed in
   some way. There are many ways that the two shuttles can be placed,
   either head-to-head, or else at right angles.  The most well-known
   and useful arrangement results in the {Gosper glider gun}.
     Other arrangements don't create any lasting output, but create
   large {spark}s which can perturb objects (especially gliders) in
   various ways.  For example, one arrangement of a queen bee shuttle
   pair was used in the original {unit Life cell} as a {memory cell}.
   Here an input glider is converted into a block, which remains until
   it is deleted by a glider on a right-angled path.
	.......................*.
	......................*..
	......................***
	.........................
	.............*...........
	............*.*..........
	............**.*.........
	............**.**........
	............**.*.........
	..**........*.*..........
	.*.*.........*....***....
	.*................***....
	**...............*...*...
	................*.....*..
	.................*...*...
	..................***....
	.........................
	.........................
	.........................
	.........................
	.........................
	.........................
	.........................
	................**.......
	.................*.......
	..............***........
	..............*..........
   See {p690 gun} and {metamorphosis II} for two more examples.

:Quetzal:  Any Herschel track-based gun with a period below 62, which is
   the lowest period with a stable glider-emitting conduit.  This was
   Dieter Leithner's name for the {true} p54 glider gun he built in
   January 1998 - a short form of {Quetzalcoatlus}, which expresses the
   fact that the gun was a very large {Herschel loop} that was not an
   {emu}.  Shortly afterwards Leithner also built a p56 Quetzal using a
   mechanism found by Noam Elkies for this purpose.  In October 1998
   Stephen Silver constructed a p55 Quetzal using Elkies' p5 {reflector}
   of the previous month.  Quetzals of periods 57-61 have since been
   constructed.
     Some of the more recent Quetzals are not Herschel loops, but are
   instead short Herschel tracks firing several glider streams all but
   one of which is reflected back to the beginning of the track to
   create a new Herschel.  Noam Elkies first had the idea of doing this
   for the p55 case, and Stephen Silver constructed the resulting gun
   shortly after building the original (much larger) p55 Quetzal. Jason
   Summers later built a p54 version, which is more complicated because
   the evenness of the period makes the timing problems considerably
   more difficult.

:Quetzalcoatlus:  A giant flying dinosaur after which Dieter Leithner
   named his p54 gun.  Usually abbreviated to {Quetzal}, or simply Q (as
   in Q54, Q55, Q56, Q-gun, etc.).

:quilt:  = {squaredance}

:R:  = {R-pentomino}

:R190:  A {composite conduit}, one of the original sixteen
   {Herschel conduit}s, discovered by Dave Buckingham in July 1996.  It
   is made up of two {elementary conduit}s, HRx131B + {BFx59H}.  After
   190 ticks, it produces a {Herschel} turned 90 degrees clockwise at
   (24, 16) relative to the input.  Its {recovery time} is 107 ticks.  A
   {ghost Herschel} in the pattern below marks the output location:
	..........**.........................
	.......**..*.........................
	.....***.**..........................
	....*................................
	.*..****.**..........................
	.***...*.**..........................
	....*................................
	...**..........................**....
	...............................*.....
	.............................*.*.....
	.............................**......
	.....................................
	.....................................
	.....................................
	.....................................
	.................................**.*
	.................................*.**
	.....................................
	*.........................**.........
	*.*.......................**.........
	***..................................
	..*..................................
	.....................................
	.....................................
	.........**...**.....................
	..........*...*......................
	.......***.....***...................
	.......*.........*...................
	.................*.*.................
	..................**.................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.........................***.........
	.........................*...........
	........................**...........

:R2D2: (p8)  This was found, in the form shown below, by Peter Raynham
   in the early 1970s.  The name derives from a form with a larger and
   less symmetric {stator} found by Noam Elkies in August 1994. Compare
   with {Gray counter}.
	.....*.....
	....*.*....
	...*.*.*...
	...*.*.*...
	**.*...*.**
	**.*...*.**
	...*...*...
	...*.*.*...
	....*.*....
	.....*.....

:r5:  = {R-pentomino}

:R64:  An {elementary conduit}, one of the original sixteen
   {Herschel conduit}s, discovered by Dave Buckingham in September 1995.
   After 64 ticks, it produces a {Herschel} rotated 90 degrees clockwise
   at (11, 9) relative to the input.  Its {recovery time} is 153 ticks,
   though this can be improved to 61 ticks by adding a from-the-side
   eater inside the turn to avoid interference from the output
   Herschel's {first natural glider}, as shown below.  A
   {ghost Herschel} in the pattern below marks the output location:
	..........**...........
	..........**.....**....
	.................**....
	.......................
	.......................
	...............**......
	...............**......
	.....................**
	.....................**
	.......................
	.......................
	.......................
	.*.....................
	.*.*...................
	.***...................
	...*...................
	.......................
	.......................
	.......................
	...**.**...............
	..*.*.*.*..............
	..*.*..*...............
	.**.*........***.......
	*...**.......*.........
	.*.*..*.*...**.........
	**.**..**..............
   R64 is one of the simplest known {Spartan} conduits, one of the two
   known {Blockic} conduits, and one of the few {elementary conduit}s in
   the original set of sixteen.  See also {p256 gun}.

:rabbits: (stabilizes at time 17331)  A 9-cell {methuselah} found by
   Andrew Trevorrow in 1986.
	*...***
	***..*.
	.*.....
   The following {predecessor}, found by Trevorrow in October 1995, has
   the same number of cells and lasts two generations longer.
	..*....*
	**......
	.**.***.

:racetrack:  A pattern in which a {signal} makes its way in a loop
   through an "obstacle course" of reactions in order to demonstrate
   various ways that the signal can be reflected, temporarily stored,
   and converted.  The more different reactions that are used the better
   the racetrack.  David Goodenough built racetracks for p30 and p46
   {technology} in 1995.  Racetracks are also known for
   {Herschel conduit} {technology}, and simple ones are useful for
   building {oscillator}s and {glider gun}s.

:rake:  Any {puffer} whose debris consists of {spaceship}s.  A rake is
   said to be forwards, backwards or sideways according to the direction
   of the spaceships relative to the direction of the rake.  Originally
   the term "rake" was applied only to forwards c/2 glider puffers (see
   {space rake}).  Many people prefer not to use the term in the case
   where the puffed spaceships travel parallel or anti-parallel to the
   puffer, as in this case they do not rake out any significant region
   of the Life plane (and, in contrast to true rakes, these puffers
   cannot travel in a stream, and so could never be produced by a
   {gun}).
     Although the first rakes (circa 1971) were c/2, rakes of other
   velocities have since been built.  Dean Hickerson's construction of
   {Cordership}s in 1991 made it easy for c/12 diagonal rakes to be
   built, although no one actually did this until 1998, by which time
   David Bell had constructed c/3 and c/5 rakes (May 1996 and September
   1997, respectively).  Jason Summers constructed a 2c/5 rake in June
   2000 (building on work by Paul Tooke and David Bell) and a c/4
   orthogonal rake in October 2000 (based largely on reactions found by
   David Bell).
     The smallest possible period for a rake is probably 7, as this
   could be achieved by a 3c/7 orthogonal backwards glider puffer.  The
   smallest period attained to date is 8 (Jason Summers' {backrake},
   March 2001).

:$rats: (p6)  Found by Dave Buckingham, 1972.
	.....**.....
	......*.....
	....*.......
	**.*.****...
	**.*.....*.*
	...*..***.**
	...*....*...
	....***.*...
	.......*....
	......*.....
	......**....

:rattlesnake: (p11)  Found by Dean Hickerson in January 2016 and named
   by Jeremy Tan.
	........**...
	........*....
	.........*...
	........**...
	.............
	.............
	.............
	.....*.......
	.....**......
	**.*.*.***...
	*.**.*.*.*...
	......*..***.
	.......**...*
	.........***.
	.........*...

:R-bee:  = {bun}.  This name is due to the fact that the pattern is a
   single-cell modification of a {beehive}.

:reaction envelope:  The collection of {cell}s that are alive during
   some part of a given active reaction.  This term is used for
   {Herschel} {circuit}s and other stable circuitry, whereas
   {construction envelope} is specific to recipes in {self-constructing}
   circuitry.
     There are some subtleties at the edges of the envelope.
   Specifically, two reactions that have the exact same set of cells
   defining their envelopes may have different behavior when placed next
   to a single-cell protrusion like the tail of an {eater1}, or one side
   of a {tub}.  The difference depends on whether two orthogonally
   adjacent cells at the edge of the envelope are ever simultaneously
   alive, within the protruding cell's {zone of influence}.

:reanimation:  A reaction performed by a {convoy} of {spaceship}s (or
   other moving objects) which converts a common stationary object into
   a glider without harming the convoy. This provides one way for
   {signal}s that have been frozen in place by some previous reaction to
   be released for use.
     Simple reactions using period 4 c/2 spaceships have been found for
   reanimating a {block}, {boat}, {beehive}, {ship}, {loaf}, {bi-block},
   or {toad}.  The most interesting of these is for a {beehive} since it
   seems to require an unusual p4 spaceship:
	..........*.......................
	.........*.*......................
	.........*.*......................
	..........*.......................
	..................................
	...............***.............***
	..............*..*.....***....*..*
	.................*....*..*.......*
	.............*...*....*...*..*...*
	.................*..*...*.*......*
	..***............*.*........**..*.
	.*..*..............*........*****.
	....*..........***...*......**....
	*...*..........................**.
	*...*.............................
	....*.............................
	.*.*...............*..............
	..................***.............
	.................**.*.............
	....*............***..............
	...***...........***..............
	...*.**..........***..............
	....***...........**..............
	....***...........................
	....**............................
     Reanimation of a {loaf} is used many times in the {Caterloopillar}.
   It is also used in the {Caterpillar} as part of its {catch and throw}
   mechanism.  Finally, reanimation can produce {rake}s from some
   {puffer}s.  See {stop and restart} for a similar idea that applies to
   {Herschel conduit}s and other {signal} {circuit}ry.
     There are small objects which have no known reanimation reactions
   using c/2 ships other than the brute force method of hitting them
   with the output of {rake}s.

:reburnable fuse:  A very rare type of {fuse} whose output is identical
   to its input, possibly with some spatial and/or temporal offset.  See
   {lightspeed wire} for an example.  Reburnable fuses are used
   primarily in the construction of fixed-speed {self-supporting}
   {macro-spaceship}s, where the speed of the fuse's burning reaction
   becomes the speed of the spaceship.  Examples include the
   {Caterpillar}, {Centipede}, and {waterbear}.

:receiver:  See {Herschel receiver}.

:recipe:  = {glider synthesis} or {construction recipe}.

:recovery time:  The number of {tick}s that must elapse after a {signal}
   is sent through a {conduit}, before another signal can be safely sent
   on the same path.  In general, a lower recovery time means a more
   useful conduit.  For example, the {Snark}'s very low recovery time
   allowed for the creation of {oscillator}s with previously unknown
   {period}s, 43 and 53.
     For the most part this is a synonym for {repeat time}.  However,
   {overclocking} a complex circuit can often allow it to be used at a
   {repeat time} much lower than its safe recovery time.

:rectifier:  The smallest known 180-degree {reflector}, discovered by
   Adam P. Goucher in 2009.  It was the smallest and fastest stable
   reflector of any kind until the discovery of the {Snark} in 2013. The
   rectifier has the same output glider as the {boojum reflector} but a
   much shorter {repeat time} of only 106 ticks.
     Another advantage of the rectifier is that the output glider is on
   a {transparent lane}, so it can be used in logic circuitry to merge
   two signal paths.
	..*.........................................
	*.*.........................................
	.**.........................................
	............................................
	..............*.............................
	.............*.*............................
	.............*.*............................
	..............*.............................
	............................................
	............................................
	............................................
	............................................
	............................................
	............................................
	............................................
	............................................
	............................................
	............................................
	............................................
	.......................**...................
	.......................**...................
	............................................
	.....**.....................................
	....*.*.....................................
	....*.......................................
	...**.......................................
	..................................**........
	.................................*..*..**...
	.................................*.*....*...
	..............**..................*.....*.**
	.............*.*.....................**.*.*.
	.............*.......................*..*..*
	............**....................*....*..**
	..................................*****.....
	............................................
	....................................**.*....
	....................................*.**....
	............................***.............
	............................*...............
	.............................*..............

:recursive filter:  A {toolkit} developed by Alexey Nigin in July 2015,
   which enables the construction of patterns with population growth
   that asymptotically matches an infinite number of different
   superlinear functions.  Toolkits enabling other, sublinear infinite
   series had been completed by Dean Hickerson and Gabriel Nivasch in
   2006.  See {quadratic filter} and {exponential filter}.
     Sublinear functions are possible using the recursive-filter toolkit
   as well.  It can be used to construct a glider-emitting pattern with
   a slowness rate S(t) = O(log***...*(t)), the nth-level iterated
   logarithm of t, which asymptotically dominates any
   primitive-recursive function f(t).

:reflector:  Any {stable} or oscillating pattern that can reflect some
   type of {spaceship} (usually a {glider}) without suffering permanent
   damage.  A pattern that is damaged or destroyed during the reflection
   process is generally called a {one-time} {turner} instead.
     The first known reflector was the {pentadecathlon}, which functions
   as a 180-degree glider reflector (see {relay}).  Other examples
   include the {buckaroo}, the {twin bees shuttle} and some oscillators
   based on the {traffic jam} reaction.  Glider {gun}s can also be made
   into reflectors, although these are mostly rather large.
     In September 1998 Noam Elkies found some fast small-period glider
   reflectors, with {oscillator}s supplying the required {domino}
   {spark}s at different periods.  A {figure-8} produced a {p8 bouncer},
   and a {p6 pipsquirter} produced an equivalent {p6 bouncer}.  A more
   complicated construction allows a {p5 bouncer} (which, as had been
   anticipated, soon led to a {true} p55 {Quetzal} gun).  And in August
   1999 Elkies found a suitable {sparker} to produce a {p7 bouncer},
   allowing the first p49 oscillator to be constructed.
     These were all called simply "p5 reflector", "p6 reflector", etc.,
   until 6 April 2016 when Tanner Jacobi discovered an equally small and
   simple reaction, the {bumper}, starting with a {loaf} as {bait}
   instead of a {boat}.  This resulted in a series of periodic
   {colour-preserving} reflectors, whereas Elkies' {bouncer} reflectors
   are all {colour-changing}.  A useful mnemonic is that "bouncer"
   contains a C and is colour-changing, whereas "bumper" contains a P
   and is colour-preserving.
     Stable reflectors are special in that if they satisfy certain
   conditions they can be used to construct {oscillator}s of all
   sufficiently large periods.  It was known for some time that stable
   reflectors were possible (see {universal constructor}), but no one
   was able to construct an explicit example until Paul Callahan did so
   in October 1996.
     Callahan's original reflector has a {repeat time} of 4840, soon
   improved to 1686, then 894, and then 850.  In November 1996 Dean
   Hickerson found a variant in which this is reduced to 747.  Dave
   Buckingham reduced it to 672 in May 1997 using a somewhat different
   method, and in October 1997 Stephen Silver reduced it to 623 by a
   method closer to the original.  In November 1998 Callahan reduced
   this to 575 with a new initial reaction.  A small modification by
   Silver a few days later brought this down to 497.
     In April 2001 Dave Greene found a 180-degree stable reflector with
   a repeat time of only 202 (see {boojum reflector}).  This reflector
   won bounties offered by Dieter Leithner and Alan Hensel.  Half of the
   prize money was recycled into a new prize for a small 90-degree
   reflector, which in turn was won by Mike Playle's {colour-preserving}
   {Snark} reflector.  The Snark is currently the smallest known stable
   reflector, with a recovery time of 43.  Playle has offered a $100
   prize for a {colour-changing} stable reflector contained within a 25
   by 25 {bounding box}, with a recovery time of 50 generations or less.
     As of June 2018, the following {splitter} is among the smallest
   known 90-degree {colour-changing} {reflector}s.  The top output can
   be blocked off by an {eater} if needed.  For small 180-degree
   colour-changing reflectors see {rectifier}, and also the sample
   pattern in {splitter}.
	................**...........*......**..................
	................**..........*.*....*..*.................
	............................*.*...*.***..**.............
	...........................**.**.*.*......*.............
	...............................*.*...**...*.*...........
	...........................**.*..****.*....**...........
	...........................**.*.*...*...................
	...............................*.*...*..................
	................................*.*...*.................
	.................................*...**..............*..
	....................................................*.*.
	.....................................................*..
	........................................................
	........................**..............................
	........................**..............................
	.........**.............................................
	........*..*............................................
	.......*.**..........................................**.
	.......*.............................................**.
	......**................................................
	.....................**.................................
	.....................*..................................
	......................***...............................
	........................*.....**........................
	.............................*.*........................
	.............................*..........................
	............................**..........................
	........................................................
	........................................................
	....................................*...............**..
	...................................*.*..............*.*.
	...................................*.*................*.
	....................................*.................**
	***.....................................**..............
	..*.....................................*.*.............
	.*........................................*.............
	..........................................**............

:reflectorless rotating oscillator:  A pattern that rotates itself 90 or
   180 degrees after some number of {generation}s, with the additional
   constraint that multiple non-interacting copies of the pattern can be
   combined into a new oscillator with a period equal to the appropriate
   fraction of the component oscillators' period. The second constraint
   disqualifies small time-symmetric {oscillator}s such as the {blinker}
   and {monogram}.
     A working RRO might look something like a {pi orbital} or
   {p256 gun} loop containing one or more {pi}s or {Herschel}s in the
   same loop, but without any external stabilisation mechanism.  Such
   patterns can be proven to exist (see {universal constructor}), but as
   of June 2018 none have been explicitly constructed in Life.  There is
   no upper limit on {multiplicity} for a constructor-based RRO.

:regulator:  An object which converts input {glider}s aligned to some
   period to output gliders aligned to a different period.  The most
   interesting case is a {universal regulator}, of which several have
   been constructed by Paul Chapman and others.

:relay:  Any {oscillator} in which {spaceship}s (typically {glider}s)
   travel in a loop.  The simplest example is the p60 one shown below
   using two {pentadecathlon}s.  Pulling the pentadecathlons further
   apart allows any period of the form 60+120n to be achieved.  This is
   the simplest proof of the existence of oscillators of arbitrarily
   large period.
	...........................*....*..
	................**.......**.****.**
	.................**........*....*..
	................*..................
	..*....*...........................
	**.****.**.........................
	..*....*...........................

:repeater:  Any {oscillator} or {spaceship}.

:repeat time:  The minimum number of generations that is possible
   between the arrival of one object and the arrival of the next.  This
   term is used for things such as {reflector}s or {conduit}s where the
   {signal} objects ({glider}s or {Herschel}s, for example) will
   interact fatally with each other if they are too close together, or
   one will interact fatally with a disturbance caused by the other.
   For example, the repeat time of Dave Buckingham's 59-step B-heptomino
   to Herschel conduit (shown under {conduit}) is 58.

:rephaser:  The following reaction that shifts the phase and path of a
   pair of gliders.  There is another form of this reaction,
   {glider-block cycle}, that reflects the gliders 180 degrees.
	..*..*..
	*.*..*.*
	.**..**.
	........
	........
	...**...
	...**...

:replicator:  A finite pattern which repeatedly creates copies of
   itself.  Such objects are known to exist (see
   {universal constructor}), but no concrete example is known.  The
   {linear propagator} may be considered to be the first example of a
   replicator built in Life, but this is debatable as each of its copies
   replicates itself only once, allowing no possibility of
   {superlinear growth}.

:reverse caber tosser:  A storage mechanism for data feeding a
   {universal constructor} designed by Adam P. Goucher in 2018.  A very
   large integer can be encoded in the position of a very faraway
   object.  If the distance to that object is measured using {circuit}ry
   designed to be as simple as possible, a complete decoder and
   universal constructor can be created by colliding a small number of
   gliders - no more than 329 according to a June 2018
   {glider synthesis}, and exactly 43 according to a July 1 redesign by
   Chris Cain using eight far-distant {GPSE}s and, amazingly, no
   stationary circuitry except for a single {catalyst} {block}.  Some
   intermediate designs with 50+ gliders need no stationary circuitry at
   all.
     With the correct placement of the faraway object, the complete
   pattern is theoretically capable of building any glider-constructible
   object.  This means that 43 is the maximum number of gliders required
   to build any constructible object, no matter what size.  However, it
   is not possible to determine in practice what the locations of these
   43 gliders should be, even for a relatively simple construction.

:reverse fuse:  A {fuse} that produces some initial debris, but then
   burns {clean}ly.  The following is a simple example.
	.............**
	............*.*
	...........*...
	..........*....
	.........*.....
	........*......
	.......*.......
	......*........
	.....*.........
	....*..........
	...*...........
	..*............
	**.............

:revolver: (p2)
	*............*
	***....*...***
	...*.*.*..*...
	..*......*.*..
	..*.*......*..
	...*..*.*.*...
	***...*....***
	*............*

:RF28B:  A {converter} with several known forms, many of which found by
   Dave Buckingham in 1972 and in the early 1980s.  It accepts an
   {R-pentomino} as input and produces an output {B-heptomino} 28 ticks
   later.  Of nine major variants known as of July 2018, four versions
   are shown below.  For each version, the R-pentomino inputs are shown
   near the left and right edges, along with the B-heptomino output
   locations near the center.
	........*..........................*........
	.......*.*.......*................*.*......*
	........*......***.................*.....***
	..............*.........................*...
	..............**........................**..
	............................................
	............................................
	......*..........*........*..........*......
	......**..........*......*..........**......
	.....**...........**....**...........**.....
	.................**......**.................
	.................*........*.................
	............................................
	............................................
	............................................
	............................................
	............................................
	............................................
	............................................
	............................................
	............................................
	............................................
	............................................
	............................................
	......*..........*........*..........*......
	......**..........*......*..........**......
	.....**...........**....**...........**.....
	.................**......**.................
	.................*........*.................
	............................................
	..*.........................................
	.*.*.............................*..........
	*..*............................*.*.........
	.**..............................**.........
     The version in the southeast is used in Paul Callahan's
   {Herschel receiver}.  The one in the northwest is part of {L156}, but
   can be replaced by the variant in the northeast which produces a
   forward glider output.

:RF48H:  Stephen Silver's alternate completion of Paul Callahan's
   {Herschel receiver}.  As of June 2018 there are four known variants.
   The original version consists of a single {loaf}.  A {ghost Herschel}
   marks the output location.
	......*..................*..
	......**.................*..
	.....**..................***
	...........................*
	............................
	.**.........................
	*..*........................
	*.*.........................
	.*..........................

:Rich's p16:  A period 16 oscillator found by Rich Holmes in July 2016,
   using {apgsearch}.  For its use as a {filter} see for example
   {p48 gun}.
	....*...*....
	..**.*.*.**..
	.*...*.*...*.
	*...**.**...*
	*.*.......*.*
	.*.........*.
	.............
	....**.**....
	...*.*.*.*...
	....*...*....


:ring of fire: (p2)  The following {muttering moat} found by Dean
   Hickerson in September 1992.
	................*.................
	..............*.*.*...............
	............*.*.*.*.*.............
	..........*.*.*.*.*.*.*...........
	........*.*.*..**.*.*.*.*.........
	......*.*.*.*......*..*.*.*.......
	....*.*.*..*..........*.*.*.*.....
	.....**.*..............*..*.*.*...
	...*...*..................*.**....
	....***....................*...*..
	..*.........................***...
	...**...........................*.
	.*...*........................**..
	..****.......................*...*
	*.............................***.
	.***.............................*
	*...*.......................****..
	..**........................*...*.
	.*...........................**...
	...***.........................*..
	..*...*....................***....
	....**.*..................*...*...
	...*.*.*..*..............*.**.....
	.....*.*.*.*..........*..*.*.*....
	.......*.*.*..*......*.*.*.*......
	.........*.*.*.*.**..*.*.*........
	...........*.*.*.*.*.*.*..........
	.............*.*.*.*.*............
	...............*.*.*..............
	.................*................

:rle:  Run-length encoded.  Run-length encoding is a simple (but not
   very efficient) method of file compression.  In Life the term refers
   to a specific ASCII encoding used for patterns in Conway's Life and
   other similar cellular automata.  This encoding was introduced by
   Dave Buckingham and is now the usual means of exchanging relatively
   small patterns by email or in online forum discussions.
     As an example of the rle format, here is a representation of the
   {Gosper glider gun}.  The "run lengths" are the numbers, b's are dead
   cells, o's are live cells, and dollar signs signal new lines:
	x = 36, y = 9, rule = B3/S23
	24bo$22bobo$12boo6boo12boo$11bo3bo4boo12boo$oo8bo
	5bo3boo$oo8bo3boboo4bobo$10bo5bo7bo$11bo3bo$12boo!
     Over the years RLE format has been extended to handle patterns with
   multiple states, neighborhoods, rules, and universe sizes.  A
   completely different encoding, {macrocell} format, is used for
   repetitive patterns that may have very large {population}s.

:R-mango:  A small active reaction, so named because it is a single-cell
   modification of a {mango}, but now more commonly known as {dove}.

:RNE-19T84:  The following {edge shooter} {converter}, accepting an
   input {R-pentomino} and producing a glider heading northeast (if the
   R-pentomino is in standard orientation).
	.................*.........
	...............***.........
	..............*............
	...*..........**...........
	..*.*......................
	..*.*......................
	.**.**....................*
	.*......................***
	..*.**.................*...
	*.*.**.................**..
	**.........................
	.............*.............
	............***.....**.....
	............*......*..*....
	....................**.....
   This converter has several common uses.  It can be attached to the
   {L156} {Herschel conduit} to change it into a useful
   {period doubler}.  Connecting it to the initial stage of the L156
   produces a composite {Herschel-to-glider} converter often used as a
   {splitter}, or as a quasi-{edge shooter} after suppressing the
   additional glider output:
	................................*.........
	..............................***.........
	.............................*............
	..................*..........**...........
	.................*.*......................
	.................*.*......................
	...............***.**....................*
	..............*........................***
	........*......***.**.................*...
	........***......*.**.................**..
	...........*..............................
	..........**..............................
	...................................**.....
	..................................*..*....
	...................................**.....
	..........................................
	..........................................
	..........................................
	.........*................................
	.........*.*..............................
	.........***..............................
	...........*...........**.................
	.......................*..................
	........................***...............
	..........................*...............
	..........................................
	..**......................................
	...*......................................
	***.......................................
	*.........................................
   The above H-to-2G mechanism appears in many places in the glider gun
   collection, for example, mainly for periods below 78 where {syringe}s
   can't be used to build small true-period guns.  The insertion
   reaction allows a glider to be placed 19 ticks in front of another
   glider on the same lane, or 30 ticks behind it (28 if the
   perpendicular glider output is suppressed.)

:rock:  Dean Hickerson's term for an {eater} which remains intact
   throughout the eating process.  The {snake} in Dave Buckingham's
   59-step B-to-Herschel conduit (shown under {conduit}) is an example.
   Other still lifes that sometimes act as rocks include the {tub}, the
   {hook with tail}, the {eater1} (eating with its tail) and the {hat}
   (in Heinrich Koenig's stabilization of the {twin bees shuttle}).

:roteightor: (p8)  Found by Robert Wainwright in 1972.  See also
   {multiple roteightors}.
	.*............
	.***........**
	....*.......*.
	...**.....*.*.
	..........**..
	..............
	.....***......
	.....*..*.....
	.....*........
	..**..*...*...
	.*.*......*...
	.*.......*....
	**........***.
	............*.

:rotor:  The cells of an {oscillator} that change state.  Compare
   {stator}.  It is easy to see that any rotor cell must be adjacent to
   another rotor cell.

:R-pentomino:  This is by far the most active {polyomino} with less than
   six cells: all the others stabilize in at most 10 generations, but
   the R-pentomino does not do so until generation 1103, by which time
   it has a {population} of 116, including six {glider}s.
	.**
	**.
	.*.
   At generation 774, an R-pentomino produces a {queen bee} which lasts
   17 more generations before being destroyed, enough time for it to
   flip over.  This observation led to the discovery of the
   {Gosper glider gun}.

:RRO:  = {reflectorless rotating oscillator}

:rule 22:  Wolfram's rule 22 is the 2-state 1-D {cellular automaton} in
   which a cell is ON in the next generation if and only if exactly one
   of its three neighbours is ON in the current generation (a cell being
   counted as a neighbour of itself).  This is the behaviour of Life on
   a cylinder of width 1.

:ruler:  A pattern constructed by Dean Hickerson in April 2005 that
   produces a stream of {LWSS} with gaps in it, such that the number of
   LWSS between successive gaps follows the "ruler function" (sequence
   A001511 in The On-Line Encyclopedia of Integer Sequences).

:rumbling river:  Any {oscillator} in which the {rotor} is connected and
   contained in a strip of width 2.  The following p3 example is by Dean
   Hickerson, November 1994.
	..............**......**......**...*.**..........
	....*........*..*....*..*....*..*..**.*..........
	*..*.*....*...**..*...**..*...*.*.....*.**.......
	****.*..******..******..******..******.*.*.......
	.....*.*.....*.*.....*.*.....*.*.....*.*......**.
	..**.*.*.*.*...*.*.*...*.*.*...*.*.*...*.*.....*.
	.*.....*.*...*.*.*...*.*.*...*.*.*...*.*.*.*.**..
	.**......*.*.....*.*.....*.*.....*.*.....*.*.....
	.......*.*.******..******..******..******..*.****
	.......**.*.....*.*...*..**...*..**...*....*.*..*
	..........*.**..*..*....*..*....*..*........*....
	..........**.*...**......**......**..............

:Rx202:  A {composite conduit}, one of the original sixteen
   {Herschel conduit}s, discovered by Dave Buckingham in May 1997.  It
   is made up of two {elementary conduit}s,  HR143B + {BFx59H}.  After
   202 ticks, it produces an inverted {Herschel} turned 90 degrees
   clockwise at (7, 32) relative to the input.  Its {recovery time} is
   201 ticks.  A {ghost Herschel} in the pattern below marks the output
   location:
	..............**...............
	...........**..*...............
	.........***.**......*.........
	........*..........***.........
	.........***.**...*............
	...........*.**...**...........
	...............................
	...............................
	...............................
	...............................
	.......................**......
	.......................*.......
	.....................*.*.......
	.....................**........
	...............................
	...............................
	...............................
	...............................
	...............................
	...*...........................
	...*.*.........................
	...***.........................
	.....*.........................
	......................**.......
	......................**.......
	...............................
	...............................
	...............................
	...............................
	...............................
	...............................
	...............................
	*.**...........................
	**.*...........................
	.....................**........
	.........**.........*..*..**...
	.........**.........*.*....*...
	.....................*.....*.**
	........................**.*.*.
	........................*..*..*
	.....................*....*..**
	.....................*****.....
	...............................
	...................*******.....
	...................*..*..*.....
	.................*.*...........
	.................**............
	...............................
	...............................
	...............................
	...............................
	...............................
	.........***...................
	...........*...................
	...........**..................

:S:  Usually means {big S}, but may sometimes mean {paperclip}.

:sailboat: (p16)  A {boat} {hassle}d by a {Kok's galaxy}, a {figure-8}
   and two {eater3}s.  Found by Robert Wainwright in June 1984.
	........*...........*........
	.......*.*.........*.*.......
	........*...........*........
	.............................
	......*****.......*****......
	.....*....*.......*....*.....
	....*..*.............*..*....
	.*..*.**.............**.*..*.
	*.*.*.....*.......*.....*.*.*
	.*..*....*.*.....*.*....*..*.
	....**..*..*.....*..*..**....
	.........**.......**.........
	.............**..............
	.............*.*.............
	........*..*..*..............
	.......*.....................
	.....**..........***.........
	..*......**.*....***.........
	.....*...*..*....***.........
	.....***.*...*......***......
	..*...........*.....***......
	...*...*.***........***......
	....*..*...*.................
	....*.**......*..............
	..........**.................
	.........*...................
	.....*..*....................

:salvo:  A collection of spaceships, usually gliders, all travelling in
   the same direction.  Any valid glider construction {recipe} can be
   partitioned into no more than four salvos.  Compare {flotilla}.  In
   contrast with a {convoy}, the spaceships in a salvo are usually
   consumed by the reactions that they cause.  Simple examples include
   {block pusher} and {block pull}.
     Salvos may be {slow} or {synchronized}.  The following partially
   {synchronized} three-glider salvo produces an {LWSS} from a block.
	**........
	**........
	..........
	..........
	***.......
	*.........
	.*........
	..........
	.......***
	.......*..
	........*.
	..........
	..........
	..........
	..........
	..........
	..........
	.......***
	.......*..
	........*.
   The above is a synchronized salvo and not a slow salvo, because the
   second glider must follow the first with the exact separation shown.
   The third glider can be considered to be a slow glider, because it
   will still delete the temporary loaf no matter how many {tick}s it is
   delayed.  The {slow glider construction} entry includes an example of
   a true slow salvo.

:sawtooth:  Any finite pattern whose {population} grows without bound
   but does not tend to infinity.  (In other words, the population
   reaches new heights infinitely often, but also infinitely often
   returns to some fixed value.)  Conway's preferred plural is
   "sawteeth".
     The first sawtooth was constructed by Dean Hickerson in April 1991.
   The current smallest known sawtooth was found by a conwaylife.com
   forum user with the online handle 'thunk'.  It has a bounding box of
   74x60, and is the smallest known sawtooth in terms of its minimum
   repeating population of 177 cells. The following variant has a higher
   repeating population of 194 and an optimized bounding box of 62x56:
	.....................................................**.*.....
	.....................................................*.**.....
	..............................................................
	...........**.................................................
	...........**.................................................
	..............................................................
	..............................................................
	..............**............................**.......**.....**
	....**........**.....................................**.....**
	.....*.....................................*.*................
	....*......**............................*..............**....
	....**.....**........................**.*.**............**....
	......................................*.**....................
	.......................................*......................
	..............................................................
	.................................**...........................
	.................................**...........................
	..............................................................
	.............................**.....**........................
	.............................**.....**........................
	..............................................................
	..............................................................
	..............................................................
	.....................***......................................
	.....................*..*.....................................
	.....................*.**.....................................
	..............................................................
	..............................................................
	..............................................................
	....................**............*.........*.................
	....................*..*..........*.*.....***.................
	..****...............***..........**.....*....................
	**....**.................................**...................
	**.....*......................................................
	..**.*.*..............**......................................
	.......*..............**......................................
	...*...*..........................*....*......................
	...*....*.......................**.....*......................
	.....***...*.....................**...*.*.....................
	.....**....*.........................**.**....................
	...........**.......................*.....*...................
	.............*.........................*......................
	.............***....................**...**...................
	..............................................................
	..............................................................
	................*.....................*.......................
	...............*.*****................*.......................
	..............**.....*...............*........................
	..............**...*..*.......................................
	......................*.......................................
	................**.*..*................**.....................
	...................*..*................**.....................
	....................**........................................
	....................**.....*....*.............................
	.........................**.****.**...........................
	...........................*....*.............................
   Patterns combining a fast {puffer} with a slower {spaceship} have
   also been constructed (see {moving sawtooth}).  See also
   {tractor beam}.

:SBM:  = {sliding block memory}

:Schick engine: (c/2 orthogonally, p12)  This {spaceship}, found by Paul
   Schick in 1972, produces a large {spark} (the 15 live cells at the
   rear in the {phase} shown below) which can be {perturb}ed by other
   c/2 spaceships to form a variety of {puffer}s.  See {blinker ship}
   for an example perturbation of the spark.  The diagram below shows
   the smallest form of the Schick engine, using two {LWSS}.  It is also
   possible to use two {MWSS}es or two {HWSS}es, or even an LWSS and an
   HWSS.
	****..............
	*...*.........*...
	*...........**....
	.*..*..**.....***.
	......***......***
	.*..*..**.....***.
	*...........**....
	*...*.........*...
	****..............

:Schick ship:  = {Schick engine}

:scorpion: (p1)
	...*...
	.***...
	*...**.
	*.*.*.*
	.**.*.*
	.....*.

:scrubber: (p2)  Found in 1971.
	....*......
	..***......
	.*.........
	.*..***....
	**.*...*...
	...*...*...
	...*...*.**
	....***..*.
	.........*.
	......***..
	......*....

:SE:  = {switch engine}

:seal: (c/6 diagonally, p6)  The first diagonal {c/6 spaceship}, found
   by Nicolay Beluchenko in September 2005.
	...*..**..........................
	.***.*.*.*........................
	.*..***..**.......................
	*..******.*.***...................
	.*..***.*.*****...................
	......*.*.*.*.....................
	*.*...*.*.*****...................
	*..*.*..*.**...*..................
	...*..**.......***................
	.*...*****.***..**................
	....*.........*...................
	..*.*.........*...................
	....**.*****...*..................
	......*.***..*.....**.............
	......*..*...*.***.**.............
	........**...***.*..*...*.........
	........**....**.****...***.......
	...................*.*..*.........
	.............*.*.....**..**.......
	.............*..*.....*.***.....*.
	.............*...*....**..*...*..*
	...............***.....**........*
	...............*.*..*..*.....**..*
	.................*..**.**.*..*....
	................*.......*.*.......
	.................*...****.........
	..................*...*...........
	..................................
	.......................*..........
	......................*.*.........
	.....................**...........
	.....................*.*..........
	.....................**...........
	.......................*..........
	......................*...........

:search program:  A computer program or script that automates the search
   for Life objects having certain desired properties.  These are used
   because the difficulty of finding previously unknown Life objects now
   commonly exceeds the patience, speed, and accuracy of humans.
   Various types of search programs are used for finding objects such as
   {spaceship}s, {oscillator}s, {drifter}s, {catalyst}s, {soup}s,
   {Garden of Eden}s, and {slow salvo}s.
     Some search programs generate {partial result}s as they are
   running, so even if they don't complete successfully, something of
   use might still be salvaged from the run.
     Example search programs are {dr}, {lifesrc}, {gfind}, and
   {Bellman}.
     There are other types of programs which don't perform searches as
   such, but instead perform large constructions.  These are used to
   correctly complete very complicated objects such as the
   {Caterpillar}, {Gemini}, {Caterloopillar}, and
   {universal constructor}-based spaceships such as the {Demonoid}s and
   {Orthogonoid}s.

:second glider domain:  The second glider domain of an {edge shooter} is
   the set of spacetime offsets, relative to the {glider} {stream}
   emitted by the edge shooter, where a second independent glider stream
   may be present without interfering with the edge shooter.  This is
   useful to know, because edge shooters are often used to generate
   glider streams very close to other glider streams, to make for
   example a {spaceship} {gun} or {converter}.

:second natural glider:  The glider produced at T=72 during the
   {evolution} of a {Herschel}.  This is the common edge-shooting glider
   output used in the {NW31} converter and several other converter
   variants.

:seed:  A {constellation} of still lifes and/or oscillators, which can
   be converted into another Life object when it is struck by one or
   more gliders.  Usually the resulting object is a rare still life or
   spaceship, more complex than the original constellation.  {Spartan}
   single-glider (1G) seeds are more commonly seen than multi-glider
   seeds, because a Spartan 1G seed can be readily constructed and
   {trigger}ed using a {slow salvo}.  See also {freeze-dried}.  For
   example, the following is a 14{sL} 1G seed for a c/7 loafer
   spaceship.
	...................................*..........
	..................................*...........
	..................................***.........
	.............**...............................
	..............*...............................
	..............*.*.............................
	...............**.............................
	..............................................
	...*..........................................
	..*.*.........................................
	.*.*..........................................
	.**...........................................
	..............**..............................
	.............*.*..............................
	.............**...............................
	..............................................
	..............................................
	..............................................
	....................**........................
	...................*.*........................
	..........*.........*.........................
	.........*.*....*.............................
	..........**...*.*............................
	..............*.*.............................
	..............**..............................
	..............................................
	.............................................*
	.........................**................***
	....................**...**...............*...
	...................*..*...................**..
	.*.................*..*.......................
	*.*.................**........................
	.**...........................................
	..............................................
	..............................................
	..............................................
	.....................**.......................
	.....................*.*....**................
	......................*.....*.*...............
	.............................**...............
	.................................**...........
	.................................**...........
	..............................................
	..............................................
	......................**......................
	.....................*..*.....................
	.....................*..*.....................
	......................**......................

:Seeds of Destruction Game:  An interactive search application written
   by Paul Chapman in 2013.  Its primary purpose was to assist in the
   design of self-destruct circuits in self-constructing circuitry.  It
   has also regularly been helpful in completing glider syntheses, and
   was used to find the {31c/240} base reaction for the {shield bug} and
   {Centipede} spaceships.

:self-constructing:  A type of pattern, generally a {macro-spaceship},
   that contains encoded construction information about itself, and
   makes a complete copy of itself using those instructions.  The
   {Gemini}, {linear propagator}, {spiral growth} patterns, {Demonoid}s
   and {Orthogonoid} are examples of self-constructing patterns.
   Self-constructing spaceships often have trivially adjustable speeds.
   In many cases, the direction of travel can also be altered, less
   easily, by changing the encoded {construction recipe}.  Compare
   {self-supporting}, {elementary}.

:self-supporting:  A type of pattern, specifically a {macro-spaceship},
   that constructs {signal}s or {track}s or other scaffolding to assist
   its movement, but does not contain complete information about its own
   structure.  Examples include the Caterpillar, {Centipede},
   {half-baked knightship}, {waterbear}, and the {Caterloopillar}s.
   {Caterpillar} has been used as a general term for self-supporting
   spaceships, but it is not very appropriate for the HBKs.
     In general a self-supporting pattern cannot be trivially adjusted
   to alter its speed or direction.  The variable speeds of the HBKs and
   the Caterloopillars are exceptions, but their direction of travel is
   fixed, and a specific Caterloopillar can't be made to change its
   speed without completely rebuilding it.  Compare {self-constructing},
   {elementary}.

:semi-cenark:  Either of two {semi-Snark} variants discovered by Tanner
   Jacobi in November 2017.  The name is due to the initial {converter},
   which produces a {century} output for every two input {glider}s.  The
   minimum safe repeat time is 43 ticks for the smaller initial
   {catalyst} shown in {CC semi-cenark} and {CP semi-cenark}, or 42
   ticks with the slightly larger catalyst variant shown below.  There
   is also {overclocking} possible at period 36, 38, or 39.  The reset
   glider can be followed immediately by a new trigger glider, as shown
   below, so the minimum repeat time for an {intermittent stream} of
   gliders is only 50 ticks.
	*.*.................................
	.**.................................
	.*..................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	.........*.*........................
	..........**........................
	..........*.........................
	.............*......................
	..............**....................
	.............**.....................
	.............................*......
	...........................***......
	..........................*.........
	..........................**........
	....................................
	....................................
	......................*.............
	..............**.......**..*........
	..............*..*....**..*.*.......
	............**..**........**........
	...........*..**....................
	...........**...**..................
	................*.*.................
	.................*..................
	..................................**
	................................*..*
	.....................**.........***.
	......................*......*......
	...................***.......****...
	...................*............*...
	...............................*....
	...............................**...

:semi-Snark:  Any small {stable} {signal} {conduit} that produces one
   output glider for every two input gliders, with a 90 degree
   reflection.  These can act as period-doublers for any glider stream
   whose period is at least equal to their repeat time, and so adding
   one of these to a single glider {gun} often results in a pattern much
   smaller than the older {technology} of crossing the output of two
   guns.
     The available semi-Snarks differ in their complexity, size, repeat
   time, and the colour of their output gliders.  The {CC semi-Snark}
   was the first one found, and the term "semi-Snark" is often used
   specifically for this object.  The "CC" prefix stands for
   {colour-changing}, by contrast with the more recently discovered
   {colour-preserving} {CP semi-Snark}.
     There are also CC and CP variants of a semi-Snark based on a
   two-{glider} to {century} {converter} discovered by Tanner Jacobi in
   November 2017.  These {semi-cenark}s are the fastest semi-Snarks
   known as of July 2018, with a {repeat time} as low as 50 ticks, or a
   periodic input rate as low as 36 ticks.

:sesquihat: (p1)  Halfway between a {hat} and a {twinhat}.
	....*..
	**.*.*.
	.*.*.*.
	.*.*.**
	..*....

:SGR:  Abbreviation for {stable} {glider} {reflector}.  This term is no
   longer in use.

:shield bug: (31c/240 orthogonally, p240)  The first 31c/240
   {macro-spaceship}, constructed by Dave Greene on September 9, 2014.

:shillelagh: (p1)
	**...
	*..**
	.**.*

:ship: (p1)  The term is also used as a synonym of {spaceship}.
	**.
	*.*
	.**
     A ship can be used as a {catalyst} in some situations.  For
   example, it can suppress two of the {blinker}s from an evolving
   {traffic light}:
	...**.
	...*.*
	....**
	......
	*.....
	**....
	*.....
   It is also a one-glider {seed} for the {engine} of the
   {queen bee shuttle}:
	***..**.
	..*..*.*
	.*....**

:ship in a bottle: (p16)  Found by Bill Gosper in August 1994. See also
   {bottle}.
	....**......**....
	...*..*....*..*...
	...*.*......*.*...
	.**..***..***..**.
	*......*..*......*
	*.**..........**.*
	.*.*..........*.*.
	...**...**...**...
	.......*.*........
	.......**.........
	...**........**...
	.*.*..........*.*.
	*.**..........**.*
	*......*..*......*
	.**..***..***..**.
	...*.*......*.*...
	...*..*....*..*...
	....**......**....

:ship on boat:  = {ship tie boat}

:ship on ship:  = {ship-tie}

:ship-tie: (p1)  The name is by analogy with {boat-tie}.
	**....
	*.*...
	.**...
	...**.
	...*.*
	....**

:ship tie boat: (p1)
	**....
	*.*...
	.**...
	...**.
	...*.*
	....*.

:short keys: (p3)  Found by Dean Hickerson, August 1989.  See also
   {bent keys} and {odd keys}.
	.*........*.
	*.***..***.*
	.*..*..*..*.
	....*..*....

:shotgun:  A {gun} that fires a {salvo} of multiple {spaceship}s, almost
   always {glider}s, on parallel {lane}s.  Two to four shotguns are
   often combined to turn a {glider synthesis} into a gun or {factory}
   for that synthesis.

:shoulder:  The fixed upper end of a {construction arm}, generally
   consisting of one or more glider {gun}s or {edge shooter}s aimed at
   an {elbow} object.

:shuttle:  Any {oscillator} which consists of an active region moving
   back and forth between stabilizing objects.  The most well-known
   examples are the {queen bee shuttle} (which has often been called
   simply "the shuttle") and the {twin bees shuttle}.  See also
   {p54 shuttle}, {p130 shuttle} and {Eureka}.  Another example is the
   p72 {R-pentomino} shuttle that forms part of the pattern given under
   {factory}.

:siamese:  A term used in naming certain {still life}s (and the {stator}
   part of certain {oscillator}s).  It indicates that the object
   consists of two smaller objects sharing two or more cells.  See
   {snake siamese snake} and {loaf siamese barge} for examples.

:side:  Half a {sidewalk}.  In itself this is unstable and requires an
   {induction coil}.
	**...
	*.***
	....*

:sidecar:  A small {tagalong} for an {HWSS} that was found by Hartmut
   Holzwart in 1992.  The resulting {spaceship} (shown below) has a
   {phase} with only 24 cells, making it in this respect the smallest
   known spaceship other than the {standard spaceship}s and some trivial
   two-spaceship {flotilla}s derived from them.  Note also that an HWSS
   can support two sidecars at once.
	.*......
	*.....*.
	*.....*.
	*****.*.
	........
	....**..
	..*....*
	.*......
	.*.....*
	.******.

:side-shooting gun:  = {slide gun}

:sidesnagger:  A {Spartan} eater found by Chris Cain in May 2015 with
   functionality similar to the {eater5}, as shown below.  It has one
   {lane} less diagonal {clearance} on the high-clearance side than
   other eater5 variants, due to the presence of the boat.  A good use
   of the sidesnagger can be seen in {p130 shuttle}.  See also
   {highway robber}.
	..*.............
	*.*.............
	.**.............
	................
	................
	................
	.........*......
	........*.......
	........***.....
	................
	................
	.........*......
	........*.*.....
	.......*..*...**
	........**....**
	....*...........
	...*.*..........
	...**...........
	.........**.....
	.........**.....

:side-tracking:  See {universal constructor}.

:sidewalk: (p1)
	.**.**
	..*.*.
	.*..*.
	.*.*..
	**.**.

:siesta: (p5)  Found by Dave Buckingham in 1973.  Compare {sombreros}.
	...........**...
	...**.....*.*...
	...*.*....*.....
	.....*...**.*...
	...*.**.....***.
	.***.....*.*...*
	*...*.*.....***.
	.***.....**.*...
	...*.**...*.....
	.....*....*.*...
	...*.*.....**...
	...**...........

:signal:  Movement of information through the Life universe.  Signals
   can be carried by {spaceship}s, {fuse}s, {drifter}s, or {conduit}s.
   Spaceships can only transfer a signal at the speed of the spaceship,
   while fuses can transfer a signal at speeds up to the
   {speed of light}.
     In practice, many signals are encoded as the presence or absence of
   a {glider} or other spaceship at a particular point at a particular
   time.  Such signals can be combined by the collision of gliders to
   form logic operations such as AND, OR, and NOT gates. Signals can be
   duplicated using {glider duplicator}s or other {fanout} devices, and
   can be used up by causing {perturbation}s on other parts of the Life
   object.
     Signals are used in {Herschel conduit} circuitry,
   {universal constructor}s, {macro-spaceship}s, and other computational
   patterns such as the {pi calculator} and {Osqrtlogt} patterns.

:signal elbow:  A {conduit} with  {signal} output 90 degrees from its
   input.  This term is commonly used only for signal {wire}s,
   particularly {2c/3} signals.  A {Snark} could reasonably be called a
   "glider elbow", but {glider reflector} is the standard term.  A
   signal elbow with a {recovery time} less than 20 ticks would enable a
   trivial proof that Conway's Life is {omniperiodic}.
     A near miss is the following elbow-like {converter} found by Dean
   Hickerson.  It successfully turns a 2c/3 signal by 90 degrees, but
   unfortunately changes it to a double-length signal in the process.
   This means that further copies of the converter can not be appended
   (e.g., to make a closed loop).
	........................*..*......
	........................******....
	..............................*.**
	......................*****.*.*.**
	.....................*......*.*...
	.....................*****..*.*...
	..................*.......*.**....
	..................******..*.......
	........................*.*.......
	................******..*.**......
	..........**...*......*.*.........
	.........*..*..*****..*.*.........
	........*.***.......*.**..........
	....**.*.*...*****..*.............
	.....*.*...*......*.*.............
	.....*.*..******..*.**............
	...*.*.*.*......*.*...............
	..*.**..*.****..*.*...............
	..*...*.*.*...*.**................
	**.**.*.*...*.*...................
	.*.*..*.****.*.***................
	*..*.*.......*...*................
	.***..********....................
	....*.*...........................
	...**.*..*******..................
	..*..**.*.......*.................
	..**....*..******.................
	........*.*.......................
	.......**.*..******...............
	..........*.*......*..............
	..........*.*..*****..............
	...........**.*.......*...........
	..............*..******...........
	..............*.*.................
	.............**.*..******.........
	................*.*......*.**.....
	................*.*..*****.**.....
	.................**.*.............
	....................*..******.....
	....................*.*.....*.....
	...................**.*..***......
	......................*.*.....**..
	......................*..*....**..
	.......................**.........
     Relatively small {composite} {MWSS} elbows can now be constructed,
   using Tanner Jacobi's 2015 discovery of a small {H-to-MWSS}
   component. For example, the {Orthogonoid} includes a
   constructor/reflector that reflects an MWSS stream by 180 degrees,
   but it can be trivially reconfigured to make a 90-degree MWSS elbow.

:Silver G-to-H:  A variant of the {Silver reflector} made by
   substituting an {Fx119} conduit for the final {NW31}, allowing a
   Herschel output as well as the beehive-annihilating reset glider.  It
   is still {Spartan}, and as long as the Fx119 is followed by a
   {dependent conduit}, it retains the faster 497-tick {recovery time}.

:Silver reflector:  A {stable} {glider reflector} found by Stephen
   Silver in November 1998, by substituting an {NW31} converter for the
   second {Fx77} conduit in the {Callahan G-to-H} found a few days
   previous.  The repeat time is 497 ticks:
	........*.............*.......................................
	......*.*...........***.......................................
	.......**..........*..........................................
	...................**.........................................
	....**........................................................
	.....*........................................................
	.....*.*......................................................
	......**..........*...........................................
	.................*.*..........................................
	.................*.*..........................................
	..................*....**.....................................
	......**...............*.*....................................
	.....*.*.................*....................................
	.....*...................**...................................
	....**........................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	...............**.............................................
	...............**.............................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	...**.........................................................
	....*.........................................................
	....*.*.......................................................
	.....**.......................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	......**...............**.....................................
	......**...............*.*....................................
	.........................*....................................
	.........................**...................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	...................*..........................................
	.................***..........................................
	................*.............................................
	................**...................**.......................
	....................**................*.......................
	.....................*................*.*.....................
	...................*...................**.....................
	...................**.........................................
	..............................................................
	..............................................................
	............................................................**
	............................................................**
	..............................................................
	......................**......................................
	...**.................**......................................
	...**.........................................................
	..............................................................
	..............................................................
	..**..........................................................
	...*..........................................................
	***............**.............................................
	*..............*..............................................
	................***...........................................
	..................*...........................................
	..............................................................
	..................................................**..........
	..................................................**..........

:Silver's p5: (p5)  The following oscillator found by Stephen Silver in
   February 2000:
	**.........
	*..........
	.*..*......
	...**......
	...*...*.**
	..*....**.*
	..**.......
     As this has no {spark}, it appears useless.  Nonetheless, in March
   2000, David Eppstein found a way to use it to reduce the size of Noam
   Elkies' p5 {reflector}.

:Simkin glider gun: (p120)  A {Herschel}-based glider gun discovered by
   Michael Simkin in April 2015.  It consists of a Herschel running
   through two {B60} conduits. In terms of its 36-cell minimum
   population, it is one of the smallest known guns, sharing the record
   with the {Gosper glider gun}. In the double-barreled form, as well as
   the {pseudo}-period, {snake}-stabilized form shown below, it is the
   absolute record holder.
	**.....**........................
	**.....**........................
	.................................
	....**...........................
	....**...........................
	.................................
	.................................
	.................................
	.................................
	......................**.**......
	.....................*.....*.....
	.....................*......*..**
	.....................***...*...**
	..........................*......
	.................................
	.................................
	.................................
	.................................
	........................*.**.....
	........................**.*.....

:single-arm:  A type of {universal constructor} using just one
   construction arm and {slow salvo} techniques to construct, usually,
   {Spartan} or near-Spartan circuitry.  Compare {two-arm}.

:single-channel:  A type of {universal constructor} discovered and
   developed by Simon Ekstrom and others starting in December 2015.  The
   initial {elbow operation} toolkit was near-minimal, with just one
   {push}, one {pull}, and one output glider of each colour (see
   {colour of a glider}).  Later searches produced a much larger and
   more efficient library.
     Single-channel {recipe}s consist of a {stream} of {glider}s on a
   single {lane} and aimed at a {construction elbow}, usually separated
   from each other by at least 90 {tick}s.  In spite of these strict
   limitations, single-channel recipes can be made to do surprising
   things.  For example, it is possible to build a {Snark} directly on
   the {construction lane} of an active construction arm, starting from
   a single {elbow} {block}.  This can allow the arm to reach
   efficiently around complex obstructions by bending itself through
   multiple {lossless elbow}s.  Known recipes can also remove an elbow
   when it is no longer needed, by controlled demolition of the Snark.
     As of June 2018, almost all single-channel recipes are made up of
   {singleton}s and {synchronized} pairs of gliders, but no synchronized
   triplets or larger groups.  This is not an inherent limitation of
   single-channel construction, but rather a limitation in the
   {search program} used to find currently known single-channel
   {toolkit}s.
     A useful byproduct of this limitation is that single-channel
   recipes can be trivially adjusted to allow them to safely cross
   perpendicular data streams, including other single-channel recipes
   (or earlier parts of the same recipe).  To avoid collisions with a
   crossing stream, each singleton glider or glider pair can safely be
   delayed by any even number of ticks, or technically by any multiple
   of the period of the current {intermediate target}.  The final result
   of the construction will not be affected.

:single-channel Demonoid:  See {Demonoid}.

:single-lane:  = {single-channel}.

:singleton:  In {single-channel} {recipe}s, a glider that is not
   {synchronized} with a neighboring glider in its {stream}.  Compare
   {glider pair}.

:singular flip flop: (p2)  Found by Robert Wainwright, July 1972.
	..*...
	..*.*.
	*....*
	******
	......
	..**..
	..**..

:sinking ship:  = {canoe}

:Sir Robin: ((2,1)c/6, p6)  The first elementary {knightship} in
   Conway's Game of Life, found by Adam P. Goucher on March 6, 2018,
   based on a partial by Tomas Rokicki.
	....**.........................
	....*..*.......................
	....*...*......................
	......***......................
	..**......****.................
	..*.**....****.................
	.*....*......***...............
	..****....**...*...............
	*.........**...................
	.*...*.........................
	......***..**..*...............
	..**.......*....*..............
	.............*.**..............
	..........**......*............
	...........**.***.*............
	..........**...*..*............
	..........*.*..**..............
	..........*..*.*.*.............
	..........***......*...........
	...........*.*.*...*...........
	..............**.*.*...........
	...........*......***..........
	...............................
	...........*.........*.........
	...........*...*......*........
	............*.....*****........
	............***................
	................**.............
	.............***..*............
	...........*.***.*.............
	..........*...*..*.............
	...........*....**.***.........
	.............****.*....**......
	.............*.****....**......
	...................*...........
	....................*..**......
	....................**.........
	.....................*****.....
	.........................**....
	...................***......*..
	....................*.*...*.*..
	...................*...*...*...
	...................*...**......
	..................*......*.***.
	...................**...*...**.
	....................****..*..*.
	......................**...*...
	.....................*.........
	.....................**.*......
	....................*..........
	...................*****.......
	...................*....*......
	..................***.***......
	..................*.*****......
	..................*............
	....................*..........
	................*....****......
	....................****.**....
	.................***....*......
	........................*.*....
	............................*..
	........................*..**..
	.........................***...
	......................**.......
	.....................***.....*.
	........................**..*.*
	.....................*..***.*.*
	......................**.*..*..
	........................*.*..**
	..........................**...
	......................***....*.
	......................***....*.
	.......................**...***
	........................**.**..
	.........................**....
	.........................*.....
	...............................
	........................**.....
	..........................*....

:six Ls: (p3)  This is a compact form of {loading dock}.
	...*...
	.***..*
	*...***
	***....
	....***
	***...*
	*..***.
	...*...

:sixty-nine: (p4)  Found by Robert Wainwright, October 1978.
	.........*...........
	........*.*..........
	.....................
	......*...**.........
	.....*.....*.........
	......*.*............
	........**......*....
	................*....
	..*.....**....***....
	..*...........**.....
	***.......**..**..***
	**......*.**....***..
	**..***.*.*.....***..
	..***................
	..***......*.........
	..........*.*........
	.....................
	........*...**.......
	.......*.....*.......
	........*.*..........
	..........**.........

:skewed quad: (p2)
	.**....
	.*...**
	..*.*.*
	.......
	*.*.*..
	**...*.
	....**.

:skewed traffic light: (p3)  Found by Robert Wainwright, August 1989.
	.............**.........
	............*..*........
	.............*.*........
	.........**...*.........
	..........*.**..........
	............*...........
	............*...........
	........................
	**........***......*....
	****.*........*...**....
	*.*..***.*....*.........
	.........*....*.***..*.*
	....**...*........*.****
	....*......***........**
	........................
	...........*............
	...........*............
	..........**.*..........
	.........*...**.........
	........*.*.............
	........*..*............
	.........**.............

:sL:  Abbreviation for {still life}, used most often in rough
   measurements of the complexity of a {Spartan} constellation.

:slide gun:  A {gun} which fires sideways from an extending arm.  The
   arm consists of streams of {spaceship}s which are pushing a pattern
   away from the body of the gun and releasing an output spaceship every
   time they do so.  Each output spaceship therefore travels along a
   different path.
     Dieter Leithner constructed the first slide gun in July 1994
   (although he used the term "side shooting gun").  The following
   pattern shows the key reaction of this slide gun.  The three gliders
   shown will push the block one cell diagonally, thereby extending the
   length of the arm by one cell, and at the same time they release an
   output glider sideways.  (In 1999, Jason Summers constructed slide
   guns using other reactions.)
	..............**.
	..............**.
	........***......
	..........*......
	.........*.....**
	..............*.*
	................*
	.................
	.................
	.................
	.................
	.................
	.................
	.................
	.................
	.................
	.................
	.*...............
	.**..............
	*.*..............

:sliding block memory:  A memory register whose value is stored as the
   position of a {block}.  The block can be moved by means of {glider}
   collisions.  See {block pusher} for an example.
     In Conway's original formulation (as part of his proof of the
   existence of a {universal computer} in Life) two gliders were used to
   pull the block inwards by three diagonal spaces, as shown below, and
   thirty gliders were used to push it out by the same amount.
	**..........
	**..........
	............
	............
	............
	.........***
	***......*..
	*.........*.
	.*..........
     Dean Hickerson later greatly improved on this, finding a way to
   pull a block inwards by one diagonal space using 2 gliders, and push
   it out the same distance using 3 gliders. In order for the memory to
   be of any use there also has to be a way to read the value held.  It
   suffices to be able to check whether the value is zero (as Conway
   did), or to be able to detect the transition from one to zero (as
   Hickerson did).
     Dean Hickerson's sliding block memory is used in Paul Chapman's
   {URM}, and the key salvos from it are used in several other complex
   constructions, such as David Bell's {Collatz 5N+1 simulator} and Adam
   P. Goucher's {pi calculator} and {Spartan}
   {universal computer}-constructor.

:slmake:  A {search program} published by Adam P. Goucher in May 2017.
   It accepts as input a {constellation} of sufficiently widely
   separated {still life}s, and produces a {glider} {stream} that will
   perform a complete {slow glider construction} of that constellation,
   starting from a single block.
     One of slmake's primary uses is to make {self-constructing}
   patterns much easier to design and build.  It is capable of finding
   {recipe}s not only for {Spartan} {stable} {circuit}ry, but also for
   other useful non-Spartan circuits such as {Snark}s, {syringe}s, and
   {H-to-MWSS} {converter}s, provided that they are separated from other
   nearby objects by a sufficient amount of empty space.

:slow:  See {slow glider construction}.

:slow elbow:  A movable {construction elbow} that is controlled by a
   {slow salvo}, which most likely comes from a previous elbow in a
   multi-elbow {construction arm}.  Unlike a standard elbow which is
   generally fixed on a single {construction lane} or at least within a
   narrow range, a slow elbow can move freely in two dimensions as long
   as there is room for it.  Each slow elbow added to a construction arm
   results in an exponential increase in the cost (in gliders) of the
   final construction.  Compare {lossless elbow}.

:slow glider construction:  Construction an object by a "slow salvo" of
   {glider}s all coming from the same direction, in such a way that
   timing of the gliders does not matter as long as they are not too
   close behind one another.  This type of construction requires an
   initial seed object, such as a {block}, which is modified by each
   glider in turn until the desired object is produced.
     In May 1997, Nick Gotts produced a slow glider construction of a
   block-laying switch engine from a block, using a slow salvo of 53
   gliders.  Constructions like this are important in the study of
   {sparse Life}, as they will occur naturally as gliders created in the
   first few generations collide with {blonk}s and other debris.
     Slow glider constructions are also useful in some designs for
   {universal constructor}s.  However, in this case the above definition
   is usually too restrictive, and it is desirable to allow
   constructions in which some gliders in the salvo are required to have
   a particular timing modulo 2 (a "p2 slow salvo").  This gives much
   greater flexibility, as {blinker}s can now be freely used in the
   intermediate construction steps.  The {Snarkmaker} is a very large p2
   slow salvo.  A much smaller example is the following {edgy}
   construction of an {eater1} starting from a block.
	**..***...............................................
	**..*.................................................
	.....*................................................
	......................................................
	......................................................
	......................................................
	......................................................
	......................................................
	......................................................
	......................................................
	................***...................................
	................*.....................................
	.................*....................................
	......................................................
	......................................................
	......................................................
	......................................................
	.......................***............................
	.......................*..............................
	........................*.............................
	......................................................
	......................................................
	......................................................
	......................................................
	......................................................
	......................................................
	......................................................
	..............................*.......................
	........................*....**.......................
	.......................**....*.*......................
	.......................*.*............................
	......................................................
	......................................................
	..........................*...........................
	.........................**...........................
	.........................*.*..........................
	......................................................
	.............................***....................**
	.............................*.....................**.
	..............................*......................*
     Adam P. Goucher's {slmake} {search program}, made available in May
   2017, makes it much easier to find a slow glider construction for a
   wide variety of {stable} {circuit}ry.

:slow salvo:  See {slow glider construction}.

:small fish:  = {LWSS}

:small lake: (p1)  A 20-cell {still life}, but technically not actually
   a {lake} because it is not constructed entirely out of {domino}es.
	....*....
	...*.*...
	...*.*...
	.**...**.
	*.......*
	.**...**.
	...*.*...
	...*.*...
	....*....

:smiley: (p8)  Found by Achim Flammenkamp in July 1994 and named by Alan
   Hensel.
	**.*.**
	...*...
	*.....*
	.*****.
	.......
	.......
	***.***

:SMM breeder:  See {breeder}.

:smoke:  Debris that is fairly long-lived but eventually dies
   completely.  Basically, a large {spark}.  This term is used
   especially when talking about the output from a {smoking ship}.  Some
   {Herschel conduit}s such as {Fx119} also create large amounts of
   smoke.

:smoking ship:  A {spaceship} which produces {smoke}.  If the smoke
   extends past the edge of the rest of the spaceship, then it can be
   used to perturb other objects as the spaceship passes by.  Running
   gliders into the smoke is often a good way to turn or duplicate them,
   or convert them into other objects.  Sometimes the smoke from a
   smoking ship may itself be perturbed by accompanying spaceships in
   order to form a {puffer}.  A simple example of a smoking ship is the
   {Schick engine}.

:snacker: (p9)  Found by Mark Niemiec in 1972.  This is a
   {pentadecathlon} with stabilizers which force it into a lower period.
	**................**
	.*................*.
	.*.*............*.*.
	..**............**..
	.......*....*.......
	.....**.****.**.....
	.......*....*.......
	..**............**..
	.*.*............*.*.
	.*................*.
	**................**
   The stabilizers make the {domino} spark largely inaccessible, but the
   snacker is {extensible}, as shown in the next diagram, and so a more
   accessible p9 domino spark can be obtained.  In April 1998 Dean
   Hickerson found an alternative stabilizer that is less obtrusive than
   the original one, and this is also shown in this diagram.
	**................................
	.*................................
	.*.*.........................**...
	..**.......................*..*...
	.......*....*..............***....
	.....**.****.**...*....*......***.
	.......*....*...**.****.**...*...*
	..**..............*....*......***.
	.*.*.......................***....
	.*.........................*..*...
	**...........................**...
   An end can also be stabilized by killer {candlefrobra}s.

:snail: (c/5 orthogonally, p5)  The first known {c/5 spaceship},
   discovered by Tim Coe in January 1996.  For some time it was the
   slowest known orthogonal spaceship.
	.*....................................
	.*....................................
	*.....................................
	.***.................***...***........
	.**.*.........*...*.*......***........
	..*...........**.*.......*....****....
	......*......*...*.*...**.*.....**....
	...*..*.***...**.........*........**.*
	...**.*.....*.....*.................*.
	.........*.*******....................
	......................................
	.........*.*******....................
	...**.*.....*.....*.................*.
	...*..*.***...**.........*........**.*
	......*......*...*.*...**.*.....**....
	..*...........**.*.......*....****....
	.**.*.........*...*.*......***........
	.***.................***...***........
	*.....................................
	.*....................................
	.*....................................

:snake: (p1)
	**.*
	*.**

:snake bit:  An alternative name for a {boat-bit}.  Not a very sensible
   name, because various other things can be used instead of a snake.  A
   snake, or alternatively an {aircraft carrier}, is the smallest object
   that can consume a glider {stream} by effectively acting as an
   {eater} for every two incoming gliders.  The one-cell reduction from
   the smallest real eater, the seven-cell {eater1}, has been important
   when trying to construct recent {sawtooth}s where the {population}
   must be minimized.

:snake bridge snake: (p1)
	....**
	....*.
	.....*
	....**
	**.*..
	*.**..

:snake dance: (p3)  Found by Robert Wainwright, May 1972.
	...**.*..
	...*.**..
	**.*.....
	.*..*.***
	*..*.*..*
	***.*..*.
	.....*.**
	..**.*...
	..*.**...

:snake pit:  This term has been used for two different {oscillator}s:
   the p2 snake pit (essentially the same as {fore and back})
	*.**.**
	**.*.*.
	......*
	***.***
	*......
	.*.*.**
	**.**.*
   and the p3 snake pit.
	.....**....
	....*..*...
	....*.**...
	.**.*......
	*.*.*.****.
	*.........*
	.****.*.*.*
	......*.**.
	...**.*....
	...*..*....
	....**.....

:snake siamese snake: (p1)
	**.**.*
	*.**.**

:Snark:  A small stable 90-degree glider reflector with a repeat time of
   43 ticks, discovered by Mike Playle on 25 April 2013 using a search
   utility he wrote called {Bellman}. Compare {boojum reflector}.  Four
   common Snark variants are shown below:  Playle's original at the top,
   and variants by Heinrich Koenig, Simon Ekstrom, and Shannon Omick to
   the left, bottom, and right, respectively.  As of June 2018, only
   Playle's variant has a known {slow glider construction} {recipe} for
   all orientations.
	.............................**....................
	............................*.*....................
	......................**....*......................
	....................*..*..**.****..................
	....................**.*.*.*.*..*..................
	.......................*.*.*.*.....................
	.......................*.*.**......................
	........................*..........................
	...................................................
	.....................................**............
	............................**.......*.............
	............................**.....*.*.............
	.........*.........................**..............
	.........***.......................................
	............*........*.............................
	...........**.......*..............................
	....................***............................
	...................................................
	...**..............................................
	...*.....................**........................
	**.*......................*........................
	*..***....**...........***.........................
	.**...*...**...........*......................*....
	...****.....................**..............*****..
	...*...............**........*.............*.....*.
	....***............*.*.......*.*............***..*.
	.......*.............*........**...............*.**
	..*****..............**.....................****..*
	.*..*......................*...........**...*...**.
	.**......................***...........**....***...
	........................*......................*...
	........................**.....................*.**
	..............................................**.**
	...................................................
	...................................................
	......................................**...........
	......................................*............
	.......................................***.........
	..............**.........................*.........
	.............*.*.....**............................
	.............*.......**............................
	............**.....................................
	...................................................
	..........................*........................
	................**....**.*.*.......................
	...............*..*..*.*.*.*.......................
	................**...*.*.*.**......................
	..................****.**..*.......................
	..................*...*....*.......................
	...................*..*.***........................
	....................*.*.*..........................
	.....................*.............................

:Snarkmaker:  A {single-channel} {stream} of {glider}s that, when aimed
   to collide with an {elbow} {block} in a specific location, will
   perform a {slow glider construction} of a {Snark}, directly on the
   same {lane} as the incoming gliders.  This allows a
   {construction arm} to add one or more {lossless elbow}s, so that it
   can bend around multiple corners without an exponential increase in
   construction cost.
     The Snarkmaker recipe used in the first single-channel {Demonoid},
   {Orthogonoid}, and {spiral growth} patterns contains 2,254 gliders.
   This could be considerably reduced with a customized
   {search program}.

:SNG:  = {second natural glider}.

:SODGame:  = {Seeds of Destruction Game}

:sombrero:  One half of {sombreros} or {siesta}.

:sombreros: (p6)  Found by Dave Buckingham in 1972.  If the two halves
   are moved three spaces closer to one another then the period drops to
   4, and the result is just a less compact form of {Achim's p4}.
   Compare also {siesta}.
	...**........**...
	...*.*......*.*...
	.....*......*.....
	...*.**....**.*...
	.***..........***.
	*...*.*....*.*...*
	.***..........***.
	...*.**....**.*...
	.....*......*.....
	...*.*......*.*...
	...**........**...

:soup:  A random initial pattern, either contained within a small area,
   or alternatively filling the whole Life universe.
     Finite soups probably have behaviors very different than infinite
   soups, but this is obviously unknown.  Infinite soups may remain
   chaotic indefinitely since any reaction, no matter how rare, is bound
   to happen somewhere.
     Soups can have an average density, with results varying based on
   that.  See {sparse Life} for a discussion of what can happen at a low
   density.
     Finite soups for sizes such as 16x16 (asymmetric) have been
   examined by the billions by scripts such as {apgsearch} to find
   interesting results.  Many new {oscillator}s and {synthesis}
   {recipe}s have been discovered, as well as previously known rare
   patterns such as {stabilized switch engine}s.  In addition, soups are
   used to generate statistical {census} data, and to decide whether
   specific objects can be considered {natural}.
     Soups can be fully random, or they can be forced to be {symmetric}.
   The results for these two types of soups can differ since symmetric
   soups tend to create large symmetrical objects at a much higher rate.
   Shown below is an unusual mirror-symmetric soup that produces a
   {pufferfish} and nothing else.
	****..**.***.*...*.***.**..****
	.*.*.**.*.............*.**.*.*.
	..***..*.*.*.......*.*.*..***..
	*.**.***.*..*.....*..*.***.**.*
	.****.*...**.*****.**...*.****.
	.....**...**.*.*.*.**...**.....
	..***...**...*...*...**...***..
	*..*..*.**...**.**...**.*..*..*
	**.*..*...*.........*...*..*.**
	*.*.*...****..***..****...*.*.*
	*.***.**..**...*...**..**.***.*
	..*.....**...*...*...**.....*..
	*****.*.***..*...*..***.*.*****
	.*....*....*..***..*....*....*.
	.**.*...***************...*.**.
	****.***......*.*......***.****

:space dust:  A part of a {spaceship} or {oscillator} which looks like a
   random mix of ON and OFF cells.  It is usually very difficult to find
   a {glider synthesis} for an object that consists wholly or partly of
   space dust.  As examples, the {295P5H1V1}, {fly}, and {seal}
   spaceships contain large amounts of space dust.

:spacefiller:  Any pattern that grows at a quadratic rate by filling
   space with an {agar}.  The first example was found in September 1993
   by Hartmut Holzwart, following a suggestion by Alan Hensel.  The
   diagram below shows a smaller spacefiller found by Tim Coe.  See also
   {Max}.  Spacefillers can be considered as {breeder}s (more precisely,
   MMS breeders), but they are very different from ordinary breeders.
   The word "spacefiller" was suggested by Harold McIntosh and soon
   became the accepted term.
	..................*........
	.................***.......
	............***....**......
	...........*..***..*.**....
	..........*...*.*..*.*.....
	..........*....*.*.*.*.**..
	............*....*.*...**..
	****.....*.*....*...*.***..
	*...**.*.***.**.........**.
	*.....**.....*.............
	.*..**.*..*..*.**..........
	.......*.*.*.*.*.*.....****
	.*..**.*..*..*..**.*.**...*
	*.....**...*.*.*...**.....*
	*...**.*.**..*..*..*.**..*.
	****.....*.*.*.*.*.*.......
	..........**.*..*..*.**..*.
	.............*.....**.....*
	.**.........**.***.*.**...*
	..***.*...*....*.*.....****
	..**...*.*....*............
	..**.*.*.*.*....*..........
	.....*.*..*.*...*..........
	....**.*..***..*...........
	......**....***............
	.......***.................
	........*..................

:space nonfiller:  Any pattern that expands indefinitely to affect every
   cell in the Life plane, but leaves an expanding region of {vacuum} at
   its center.  Compare {spacefiller}; see also {antstretcher}.  The
   first nonfiller was discovered by Jason Summers on 14 April 1999:
	...................***...............
	..................*..*...............
	............***......*....***........
	............*..*.*...*....*..*.......
	............*..*.*...*....*..*.......
	..........*..........*..*.*.***......
	..........**..**..*.*....*.....*.....
	........*................**..***.....
	........***.*.**..........*......*...
	......*........*.........*.*...***...
	......***.....*..........*........*..
	...*.*.........................*.***.
	..*****.*..........................*.
	.**......*.....................*****.
	**....**..................*.*........
	.*.*...*..*...............*..*...*.*.
	........*.*..................**....**
	.*****.....................*......**.
	.*..........................*.*****..
	.***.*.........................*.*...
	..*........*..........*.....***......
	...***...*.*.........*........*......
	...*......*..........**.*.***........
	.....***..**................*........
	.....*.....*....*.*..**..**..........
	......***.*.*..*..........*..........
	.......*..*....*...*.*..*............
	.......*..*....*...*.*..*............
	........***....*......***............
	...............*..*..................
	...............***...................

:space rake:  The following p20 forwards glider {rake}, which was the
   first known rake.  It consists of an {ecologist} with a {LWSS} added
   to turn the dying debris into {glider}s.
	...........**.....****
	.........**.**...*...*
	.........****........*
	..........**.....*..*.
	......................
	........*.............
	.......**........**...
	......*.........*..*..
	.......*****....*..*..
	........****...**.**..
	...........*....**....
	......................
	......................
	......................
	..................****
	*..*.............*...*
	....*................*
	*...*............*..*.
	.****.................

:spaceship:  Any finite pattern that reappears (without additions or
   losses) after a number of generations and displaced by a non-zero
   amount.  By far the most {natural} spaceships are the {glider},
   {LWSS}, {MWSS} and {HWSS}, followed by the {Coe ship} which has also
   evolved multiple times from random asymmetric {soup} starting
   conditions.  See also the entries on individual spaceship speeds:
   {c/2 spaceship}, {c/3 spaceship}, {c/4 spaceship}, {c/5 spaceship},
   {c/6 spaceship}, {c/7 spaceship}, {c/10 spaceship}, {c/12 spaceship},
   {2c/5 spaceship},  {2c/7 spaceship}, {3c/7 spaceship},
   {(2,1)c/6 spaceship}, and {17c/45 spaceship}.
     It is known that there exist spaceships travelling in all rational
   directions and at arbitrarily slow speeds (see
   {universal constructor}).  Before 1989, however, the only known
   examples travelled at c/4 diagonally (gliders) or c/2 orthogonally
   (everything else).
     In 1989 Dean Hickerson started to use automated searches to look
   for new {elementary} spaceships, and had considerable success.  Other
   people have continued these searches using tools such as {lifesrc}
   and {gfind}, and as a result we now have a great variety of
   elementary spaceships travelling at sixteen different velocities.
   The following table details the discovery of elementary spaceships
   with new velocities as of July 2018.

   -------------------------------------------------------------------
	Speed    Direction  First Discovery     Discoverer
   Date

   -------------------------------------------------------------------
	c/4      diagonal   {glider}            Richard Guy
   1970
	c/2      orthogonal {LWSS}              John Conway
   1970
	c/3      orthogonal {25P3H1V0.1}        Dean Hickerson     Aug
   1989
	c/4      orthogonal {119P4H1V0}         Dean Hickerson     Dec
   1989
	c/12     diagonal   {Cordership}        Dean Hickerson     Apr
   1991
	2c/5     orthogonal {44P5H2V0}          Dean Hickerson     Jul
   1991
	c/5      orthogonal {snail}             Tim Coe            Jan
   1996
	2c/7     orthogonal {weekender}         David Eppstein     Jan
   2000
	c/6      orthogonal {dragon}            Paul Tooke         Apr
   2000
	c/5      diagonal   {295P5H1V1}         Jason Summers      Nov
   2000
	c/6      diagonal   {seal}              Nicolay Beluchenko Sep
   2005
	c/7      diagonal   {lobster}           Matthias Merzenich Aug
   2011
	c/7      orthogonal {loafer}            Josh Ball          Feb
   2013
	c/10     orthogonal {copperhead}        zdr                Mar
   2016
	3c/7     orthogonal {spaghetti monster} Tim Coe            Jun
   2016
	(2,1)c/7 oblique    {Sir Robin}         Adam P. Goucher    Mar
   2018

   -------------------------------------------------------------------
     Several infinite families of adjustable-velocity {macro-spaceship}s
   have also been constructed, of which the first was Gabriel Nivasch's
   {Caterpillar} from December 2004.  The macro-spaceship with the
   widest range of possible speeds is Michael Simkin's {Caterloopillar}
   from April 2016; in theory it supports any rational orthogonal speed
   strictly less than c<4.  A somewhat similar design supporting any
   rational speed strictly less than c/2 has been shown to be feasible,
   but as of July 2018 no explicit examples have been constructed.
     A period p spaceship that displaces itself (m,n) during its period,
   where m>=n, is said to be of type (m,n)/p.  It was proved by Conway
   in 1970 that p>=2m+2n.  (This follows immediately from the
   easily-proved fact that a pattern cannot advance diagonally at a rate
   greater than one half diagonal step every other generation.)

:Spaceships in Conway's Life:  A series of articles posted by David Bell
   to the newsgroup comp.theory.cell-automata during the period
   August-October 1992 that described many of the new {spaceship}s found
   by himself, Dean Hickerson and Hartmut Holzwart.  Bell produced an
   addendum covering more recent developments in 1996.

:spaghetti monster:  The first {3c/7 spaceship}, found by Tim Coe in
   June 2016.  The spaceship travels orthogonally, has a minimum of 702
   live cells and fits in a 27x137 bounding box.

:spark:  A pattern that dies.  The term is typically used to describe a
   collection of cells periodically thrown off by an {oscillator} or
   {spaceship}, but other dying patterns, particularly those consisting
   or only one or two cells (such as produced by certain glider
   collisions, for example), are also described as sparks.  For examples
   of small sparks see {unix} and {HWSS}.  Examples of much larger
   sparks are seen in {Schick engine} and {twin bees shuttle spark}.

:spark coil: (p2)  Found in 1971.
	**....**
	*.*..*.*
	..*..*..
	*.*..*.*
	**....**

:sparker:  An {oscillator} or {spaceship} that produces {spark}s. These
   can be used to {perturb} other patterns without being themselves
   affected.

:sparking eater:  One of two {eater}s found in April 1997 and November
   1998 by Dean Hickerson using his {dr} {search program}, shown below
   to the left and right respectively.  These both absorb {glider}s as a
   standard eater does, but also produce separated single-bit {spark}s
   at the upper right, which can be used to delete antiparallel gliders
   with different phases as shown.
	..*.........**........*..........**.
	*.*........**.......*.*..........*.*
	.**..........*.......**..........*..
	....**..**...............**..**.....
	.*...*..**............*...*..**.....
	.****.............**..****..........
	..................*.................
	.**................*****............
	.**.....................*...........
	.....................***............
	.....................*..............
   The above mechanisms can be used to build {intermitting glider gun}s.
   The left-hand eater produces a spark nine ticks after a glider
   impact, with the result that the period of the constituent guns can't
   be a multiple of 4.  The right-hand eater produces the same spark ten
   ticks after impact, which allows p4N guns to be used.
     The separation of the spark also allows this reaction to perform
   other {perturbation}s "around the corner" of some objects.  For
   example, it was used by Jason Summers in 2004 to cap the ends of a
   row of ten {AK47 reaction}s to form a much smaller period 94 glider
   gun than the original one.  (This is now made obsolete by the
   {AK94 gun}.)

:sparky:  A certain c/4 {tagalong}, shown here attached to the back of a
   {spaceship}.
	..........*....................
	..........*...............**...
	......**.*.***..........**...*.
	*.**.**.**..*.*...**.****......
	*...**..*.**..***..*.**..**...*
	*.**....***.*.***......**..*...
	........**.*...............*..*
	*.**....***.*.***......**..*...
	*...**..*.**..***..*.**..**...*
	*.**.**.**..*.*...**.****......
	......**.*.***..........**...*.
	..........*...............**...
	..........*....................

:sparse Life:  This refers to the study of the evolution of a Life
   universe which starts off as a random {soup} of extremely low
   density.  Such a universe is dominated at an early stage by {block}s
   and {blinker}s (often referred to collectively as {blonk}s) in a
   ratio of about 2:1.  Much later it will be dominated by simple
   {infinite growth} patterns (presumably mostly {switch engine}s).  The
   long-term fate of a sparse Life universe is less certain.  It may
   possibly become dominated by self-reproducing patterns (see
   {universal constructor}), but it is not at all clear that there is
   any mechanism for these to deal with all the junk produced by switch
   engines.

:Spartan:  A pattern composed of subunits that can be easily constructed
   in any orientation, usually with a {slow salvo}. Generally this means
   that the pattern is a {constellation} of Spartan still lifes:
   {block}, {tub}, {boat}, {hive}, {ship}, {loaf}, {eater1}, or {pond}.
   Other small objects may sometimes be counted as Spartan, including
   period-2 oscillators - mainly {blinker}s, but also {beacon}s or
   {toad}s, which may occur as {intermediate target}s in slow salvo
   {recipe}s.  Most {self-constructing} patterns are Spartan or mostly
   Spartan, to simplify the process of self-construction.

:speed booster:  Any mechanism which allows a {signal} (indicated by the
   presence or absence of a spaceship) to move faster than the spaceship
   could travel through empty space.  The original speed booster is
   based on p30 {technology}, and is shown below:
	....................*........................
	.....................*.......................
	...................***.......................
	.............................................
	...........................*.*...............
	.........................*...*...............
	.................*.......*...................
	................****....*....*........**.....
	...............**.*.*....*............**.....
	....**........***.*..*...*...*...............
	....**.........**.*.*......*.*...............
	................****.........................
	.................*...........................
	..........................***................
	..........................*.*...**...........
	.........................**.....*..*.........
	..................*.*.....*.........*......**
	................*...*..**...........*......**
	.........**.....*..........*........*........
	.*.......**....*....*.......**..*..*.........
	..*.............*.......*.*..*..**...........
	***.............*...*.....***................
	..................*.*........................
   Here the top glider is boosted by passing through two
   {inline inverter}s, emerging 5 cells further along than the unboosted
   glider at the left.
     The fastest speed boosters are the {telegraph} and {p1 telegraph},
   which can transfer a orthogonal signal at the {speed of light},
   although their bit rate is rather slow.
     Diagonal speed boosters have also been built using {2c/3 wire}s or
   other stable components.  See {stable pseudo-Heisenburp}.
     The {star gate} seems like it can transfer a signal faster than the
   {speed of light}.  The illusion is explained in
   {Fast Forward Force Field}.

:speed of light:  The greatest speed at which any effect can propagate;
   in {Life}, a speed of one cell per {generation}.  Usually denoted c.

:S-pentomino:  Conway's name for the following {pentomino}, which
   rapidly dies.
	..**
	***.

:spider: (c/5 orthogonally, p5)  This is the smallest known c/5
   {spaceship}, and was found by David Bell in April 1997.  Its side
   {spark}s have proved very useful in constructing c/5 {puffer}s,
   including {rake}s.  See also {PPS}.
	......*...***.....***...*......
	...**.*****.**...**.*****.**...
	.*.**.*.....*.*.*.*.....*.**.*.
	*...*.*...*****.*****...*.*...*
	....***.....**...**.....***....
	.*..*.***.............***.*..*.
	...*.......................*...

:spiral: (p1)  Found by Robert Wainwright in 1971.
	**....*
	.*..***
	.*.*...
	..*.*..
	...*.*.
	***..*.
	*....**

:spiral growth:  A {self-constructing} pattern built by Dave Greene in
   August 2014 that uses four {universal constructor}s (UCs) arranged in
   a diamond to build four more UCs in a slightly larger diamond.  This
   was the first B3/S23 pattern that exhibited spiral growth.  Much
   smaller versions have now been constructed using the {single-channel}
   construction toolkit.

:splitter:  A {signal} {converter} that accepts a single input signal
   and produces two or more output signals, usually of the same type as
   the input.  An older term for this is {fanout}, or "fanout device".
     A sub-category is the {one-time} splitter, which is not technically
   a converter because it can only be used once.  One-time splitters are
   usually small {constellation}s that produce two or more {clean}
   gliders when struck by a single glider.  In other words, they are
   multi-glider {seed}s.  These are important for constructing
   self-destruct circuitry in {self-constructing} spaceships.
     The following combination, a {syringe} attached to an SE7T14
   {converter} combined with an {NW31} converter, is one of the smallest
   known glider splitters as of July 2018.  Another small splitter with
   a 90-degree {colour-changing} output is shown under {reflector}.
	..........**...........*......**....................
	..........**..........*.*....*..*...................
	......................*.*...*.***...*...............
	.....................**.**.*.*......***.............
	.........................*.*...**......*............
	.....................**.*..****.*.....**............
	.....................**.*.*...*.....................
	.........................*.*...*....................
	..........................*.*...*...................
	...........................*...**...................
	....................................................
	....................................................
	....................................................
	..................**................................
	..................**................................
	...**...............................................
	..*..*..............................................
	.*.**...............................................
	.*................................................**
	**................................................**
	...............**...................................
	...............*....................................
	................***.................................
	..................*..........**.....................
	............................*.*.....................
	............................*.......................
	...........................**.......................
	***.................................................
	..*.................................................
	.*..................................................

:SPPS: (c/5 orthogonally, p30)  The symmetric {PPS}.  The original PPS
   found by David Bell in May 1998.  Compare {APPS}.

:sqrtgun:  Any glider-emitting pattern which emits its nth glider at a
   time asymptotically proportional to n^2.  The first examples were
   constructed by Dean Hickerson around 1991.  See also
   {quadratic filter}, {exponential filter}, {recursive filter}.

:squaredance:  The p2 {agar} formed by tiling the plane with the
   following pattern.  Found by Don Woods in 1971.
	**......
	....**..
	..*....*
	..*....*
	....**..
	**......
	...*..*.
	...*..*.

:squirter:  = {pipsquirter}

:S-spiral:  = {big S}

:stabilized switch engine:  A single {switch engine} which survives
   indefinitely by interacting with the appropriate {exhaust} such that
   it prevents the engine from ever being destroyed.
     The only known types of stabilized switch engines were found by
   Charles Corderman soon after he discovered the switch engine itself.
   There is a p288 block-laying type (the more common of the two) and
   the p384 glider-producing type.  These two puffers are the most
   {natural} infinite growth patterns in Life.  As of June 2018 they are
   the basis for every infinite growth pattern ever seen to occur from a
   random asymmetric {soup}, even after trillions of {census} results by
   {apgsearch} and similar projects.
     Patterns giving rise to block-laying switch engines can be seen
   under {infinite growth}, and one giving rise to a glider-producing
   switch engine is shown under {time bomb}.
     Here is the block-laying type showing its distinctive zig-zag trail
   of blocks.
	..*.........................................................
	.*.*........................................................
	............................................................
	.*..*.......................................................
	...**.......................................................
	....*.......................................................
	..................**........................................
	..................**........................................
	............................................................
	............................................................
	.**.........................................................
	...*........................................................
	..**........................................................
	.***...............*........................................
	.**................**.....**................................
	***.*..............**.....**................................
	.*...*..........**..........................................
	...*..*..........*..........................................
	...***............*.........................................
	....**........**............................................
	..............**............................................
	............................................................
	..................................**........................
	..................................**........................
	............................................................
	............................................................
	......**....................................................
	......**................**..................................
	........................**..................................
	............................................................
	..........................................**................
	....................**....................**................
	....................**......................................
	............................................................
	..............**............................................
	..............**............................................
	.......................................**...................
	.......................................**...................
	............................................................
	............................................................
	...................................**.......................
	...................................**.......................
	............................................................
	............................................................
	............................................................
	............................................................
	..........................................................**
	..........................................................**
	............................................................
	............................................................
	..............................**............................
	..............................**................**..........
	................................................**..........
	............................................................
	............................................................
	............................................**..............
	............................................**..............
	............................................................
	......................................**....................
	......................................**....................

:stable:  A pattern is said to be stable if it is a {parent} of itself.
   Stable objects are oscillators with period 1 (p1), and are generally
   called {still life}s.

:stable pseudo-Heisenburp:  A multi-stage {converter} constructed by
   Dave Greene in January 2007, using a complex recipe found by Noam
   Elkies to insert a signal into a {2c/3 wire}.  The wire's high
   transmission speed allows a {signal} from a {highway robber} to catch
   up to a {salvo} of {glider}s.  Ultimately the mechanism restores the
   key glider, which was destroyed by the highway robber in the first
   stage of the converter, to its exact original position in the salvo.
     Much smaller stable pseudo-Heisenburp devices have since been
   designed that use simple 0-degree glider {seed} {constellation}s
   instead of a 2c/3 wire.
     These patterns are labeled "pseudo-Heisenburp", because a true
   {Heisenburp device} does not even temporarily damage or affect a
   passing glider, yet can still produce an output {signal} in response.
   However, it is impossible to construct a {stable} device that can
   accomplish this for gliders.  True stable Heisenburp devices are
   possible with many other types of {spaceship}s, but not with gliders
   which have no usable side {spark}s to initiate an output signal.

:staged recovery:  A type of signal-processing {circuit} where the
   initial reaction between {catalyst}s an incoming signal results in an
   imperfect recovery.  A catalyst is damaged, destroyed completely as
   in a {bait} reaction, or one or more objects are left behind that
   must be cleaned up before the circuit can be reused.  In any of these
   three cases, output signals from the circuit must be used to complete
   the cleanup.  In theory the cleanup process might itself be {dirty},
   requiring additional cleanup stages.  In rare cases this might
   theoretically allow the construction of special-purpose circuits with
   a lower {recovery time} than would otherwise be possible, but in
   practice this kind of situation does not commonly arise.
     An example is the record-breaking (at the time) 487-tick reflector
   constructed by Adam P. Goucher on 12 April 2009.  487 ticks was a
   slight improvement over the repeat time of the {Silver reflector}.
   The reflector featured a standard {Callahan G-to-H}, with cleanup by
   an internal {dirty} glider reflector found by Dieter Leithner many
   years before.  This in turn was cleaned up by the usual ungainly
   Herschel plumbing attached to the G-to-H's output.  The dirty glider
   reflector is not actually fully recovered before a second p487 signal
   enters the full reflector.  However, it has been repaired by the time
   the internal reflector is actually needed again, so the cycle can be
   successfully repeated at p487 instead of p497.

:stairstep hexomino: (stabilizes at time 63)  The following
   {predecessor} of the {blockade}.
	..**
	.**.
	**..

:stamp collection:  A collection of {oscillator}s (or perhaps other Life
   objects) in a single diagram, displaying the exhibits much like
   stamps in a stamp album.  The classic examples are by Dean Hickerson
   (see {http://conwaylife.com/ref/DRH/stamps.html}).
     Many stamp collections contain "fonts" made of single cells (which
   cleanly die) to annotate the objects or to draw boxes around them.
   For example, here is a stamp collection which shows all the ways that
   two gliders can create a {loaf} or an {eater}:
	.*......*.*.....*....*.*.*...................*.
	............................................*..
	.*.....*...*...*.*...*......................***
	...............................................
	.*.....*...*..*...*..*.*.*.....................
	...............................................
	.*.....*...*..*.*.*..*.........................
	........................................**.....
	.*.*.*..*.*...*...*..*.................*.*.....
	.........................................*.....
	...............................................
	...............................................
	.............................................*.
	............................................*..
	*.*.*....*....*.*.*..*.*.*..*.*.............***
	................................*..............
	*.......*.*.....*....*......*..................
	................................*..............
	*.*.*..*...*....*....*.*.*..*.*................
	...............................................
	*......*.*.*....*....*......*..*...........*...
	..........................................**...
	*.*.*..*...*....*....*.*.*..*...*.........*.*..
     Alternatively, stamp collections can use {LifeHistory} for their
   annotations, but this requires a more sophisticated Life program to
   handle.  Numbers, or more rarely letters, are sometimes constructed
   from stable components such as {block}s or {snake}s, but their
   readability is somewhat limited by placement constraints.

:standard spaceship:  A {glider}, {LWSS}, {MWSS} or {HWSS}.  These have
   all been known since 1970.

:star: (p3)  Found by Hartmut Holzwart, February 1993.
	.....*.....
	....***....
	..***.***..
	..*.....*..
	.**.....**.
	**.......**
	.**.....**.
	..*.....*..
	..***.***..
	....***....
	.....*.....

:star gate:  A device by Dieter Leithner (October 1996) for transporting
   a {LWSS} faster than the {speed of light}.  The key reaction is the
   {Fast Forward Force Field}.

:stator:  The cells of an {oscillator} that are always on.  Compare
   {rotor}.  (The stator is sometimes taken to include also some of
   those cells which are always off.)  The stator is divided into the
   {bushing} and the {casing}.
     By analogy, the cells of an {eater} that remain on even when the
   eater is eating are considered to constitute the stator of the eater.
   This is not always well-defined, because an eater can have more than
   one eating action.

:statorless:  A statorless {oscillator} is one in which no cell is
   permanently on - that is, the {stator} is empty,  or in other words
   the oscillator has the maximum possible volatility.  See the
   {volatility} entry for examples of this type of oscillator at
   different periods.  Statorless oscillators can be constructed for any
   sufficiently large period, using {universal constructor} technology.

:statorless p5: (p5)  Found by Josh Ball, June 2016.  The first and only
   known {statorless} {period} 5 {oscillator}.
	*.............*
	.**.........**.
	*....**.**....*
	**.*.......*.**
	.*.*..*.*..*.*.
	..*.*.....*.*..
	..***.....***..
	..***.....***..
	..*.*.....*.*..
	.*.*..*.*..*.*.
	**.*.......*.**
	*....**.**....*
	.**.........**.
	*.............*

:step:  Another term for a {generation} or {tick}.  This term is
   particularly used in describing {conduit}s.  For example, a 64-step
   conduit is one through which the active object takes 64 generations
   to pass.

:stillater: (p3)  Found by Robert Wainwright, September 1985. This is
   one of only three essentially different p3 {oscillator}s with only
   three cells in the {rotor}.  The others are {1-2-3} and {cuphook}.
	...*....
	..*.*.**
	..*.**.*
	**......
	.*.*.**.
	.*.*..*.
	..*..*..
	...**...

:still life:  Any {stable} pattern, usually assumed to be finite and
   nonempty.  For the purposes of enumerating still lifes this
   definition is, however, unsatisfactory because, for example, any pair
   of blocks would count as a still life, and there would therefore be
   an infinite number of 8-bit still lifes.
     For this reason a stricter definition is often used, counting a
   stable pattern as a {strict still life} only if its {island}s cannot
   be divided into two or more nonempty sets both of which are stable in
   their own right. If such a subdivision can be made, the pattern can
   be referred to as a {constellation}. If its cells form a single
   {cluster} it is also, more specifically, either a {pseudo still life}
   or a {quasi still life}.
     In rare cases above a certain size threshold, a pattern may be
   divisible into three or four stable nonempty subsets but not into
   two.  See the 32-bit {triple pseudo} (32 bits) and the 34-bit
   {quad pseudo} for examples.
     All still lifes up to 18 bits have been shown to be
   {glider constructible}.  It is an open question whether all still
   lifes can be incrementally constructed using glider collisions.  For
   a subset of small still lifes that have been found to be especially
   useful in {self-constructing} circuitry, see also {Spartan}.
     The smallest still life is the {block}.  Arbitrarily large still
   lifes are easy to construct, for example by extending a {canoe} or
   {barge}.  The maximum density of a large still life is 1/2, which can
   be achieved by an arbitrarily large patch of {zebra stripes} or
   {chicken wire}, among many other options.  See {density} for more
   precise limits.
	...*..*..*..*..*..*...
	.********************.
	*....................*
	**********************
	......................
	**********************
	*....................*
	.********************.
	......................
	.********************.
	*....................*
	**********************
	......................
	**********************
	*....................*
	.********************.
	......................
	.********************.
	*....................*
	**********************
	......................
	**********************
	*....................*
	.********************.
	...*..*..*..*..*..*...

:still life tagalong:  A {tagalong} which takes the form of a
   {still life} in at least one {phase}.  An example is shown below.
	..**...............
	.**.**.............
	..****.............
	...**..............
	...................
	...*****...........
	..*******..........
	.**.*****..........
	..**...............
	...................
	........*.*.....**.
	......*....*...*..*
	......**.....*.*..*
	.*..*..****.*...**.
	*.......**.........
	*...*..............
	****...............

:stop and go:  A pattern by Dean Hickerson in which a period 46
   {shuttle} converts a glider into a block on one oscillation, and then
   converts the block back into a glider on the next oscillation.  The
   glider is reflected back onto its own path, but with a delay.
	........................................*.
	.......................................*..
	**..............**.........**..........***
	**...............**........**.............
	.............*****........................
	.............****.........................
	..........................................
	.............****.........................
	.............*****........................
	**...............**.......................
	**..............**........................

:stop and restart:  A type of {signal} {circuit} where an input signal
   is converted into a stationary object, which is then re-activated by
   a secondary input signal.  This can be used either as a memory device
   storing one bit of information, or as a simple delay mechanism.  In
   the following January 2016 example by Martin Grant, a
   {ghost Herschel} marks the output signal location, and a "ghost
   {beehive}" marks the location of the intermediate still life.
	........................................................*.
	.......................................................*..
	.......................................................***
	..........................................................
	..........................................................
	..........................................................
	..........................................................
	..........................................................
	..........................................................
	..........................................................
	..........................................................
	..........................................................
	..........................................................
	..........................................................
	..........................................................
	............*.............................................
	............***...........................................
	...............*..........................................
	..............**..........................................
	........*.................................................
	.......*.*.......**.......................................
	.......*.*......*.*.......................................
	.....***.**.....**........................................
	....*.....................................................
	.....***.**...............................................
	.......*.**...............................................
	..........................................................
	..........................................................
	..........................................................
	**........................................................
	.*........................................................
	.*.*......................................................
	..**......................................................
	..........................................................
	....................*.....................................
	...................*.*....................................
	...................*...................................*..
	....................*................................***..
	....................................**...............*....
	..*.................................**...............*....
	..*.*.....................................................
	..***.....................................................
	....*....................*................................
	........................*.*...............................
	........................**................................
	...................**............**.......................
	...................**............*........................
	..................................*.......................
	.................................**.......................
	..........................................................
	..........................................................
	..........................................................
	..........................................................
	..........................................................
	..........................................................
	..**..........**..........................................
	...*..........*...........................................
	***............***........................................
	*................*........................................
   The {eater1} in the lower left corner catches the restart glider if
   no input signal has come in to create the beehive.  This eater could
   be removed if it is useful to have both a "0" and a "1" output for a
   memory cell mechanism.
     The {catch and throw} {technology} in a {Caterpillar} is a somewhat
   similar idea.  See also {stop and go} and {reanimation}.

:stream:  A line of identical objects (usually {spaceship}s), each of
   which is moving in a direction parallel to the line, generally on the
   same {lane}.  In many uses the stream is periodic.  For example, the
   {new gun} produces a period 46 {glider} stream.  The stream produced
   by a {pseudo-random glider generator} can have a very high period.
   Compare with {wave}.  See also {single-channel} for a common use of
   non-periodic {glider} streams.

:stretcher:  Any pattern that grows by stretching a {wick} or {agar}.
   See {wickstretcher} and {spacefiller}.

:strict still life:  A {still life} that is either a single connected
   {polyplet}, or is arranged such that a {stable} smaller pattern
   cannot be formed by removing one or more of its {island}s. For
   example, {beehive with tail} is a strict still life because it is
   connected, and {table on table} is a strict still life because
   neither of the {table}s are stable by themselves.  See also
   {triple pseudo}, {quad pseudo}.
     Still lifes have been enumerated by Conway (4-7 bits), Robert
   Wainwright (8-10 bits), Dave Buckingham (11-13 bits), Peter Raynham
   (14 bits), Mark Niemiec (15-24 bits), and Simon Ekstrom and Nathaniel
   Johnston (25-32 bits).  The resulting figures are shown below; see
   also {https://oeis.org/A019473}.  The most recent search by Nathaniel
   Johnston has also confirmed that the {triple pseudo} pattern found by
   Gabriel Nivasch is the only such still life with 32 bits or less.  It
   is therefore included in the pseudo still life count and not in the
   table below.
	--------------
	Bits    Number
	--------------
	 4           2
	 5           1
	 6           5
	 7           4
	 8           9
	 9          10
	10          25
	11          46
	12         121
	13         240
	14         619
	15        1353
	16        3286
	17        7773
	18       19044
	19       45759
	20      112243
	21      273188
	22      672172
	23     1646147
	24     4051711
	25     9971377
	26    24619307
	27    60823008
	28   150613157
	29   373188952
	30   926068847
	31  2299616637
	32  5716948683
	--------------
     As the number of bits increases, the strict still life count goes
   up exponentially by approximately O(2.46^n).  By comparison, the rate
   for pseudo still life}s is about O(2.56^n) while for
   {quasi still life}s it's around O(3.04^n).

:strict volatility:  A term suggested by Noam Elkies in August 1998 for
   the proportion of cells involved in a period n {oscillator} which
   themselves oscillate with period n.  For prime n this is the same as
   the ordinary {volatility}.  Periods with known strictly-volatile
   oscillators include 1, 2, 3, 5, 6, 8, 13, 15, 22, 30, 33, and 177.
   Examples include {figure-8}, {Kok's galaxy}, {smiley}, and
   {pentadecathlon}.  A composite example is the following p22, found by
   Nicolay Beluchenko on 4 March 2009:
	...........**...
	..........*.*...
	..*.....*....*..
	**.**..**.*.*...
	*.......*...*...
	.*.*............
	................
	..***.......*...
	...*.......***..
	................
	............*.*.
	...*...*.......*
	...*.*.**..**.**
	..*....*.....*..
	...*.*..........
	...**...........

:super beehive:  = {honeycomb}

:superfountain: (p4)  A p4 {sparker} which produces a 1-cell spark that
   is separated from the rest of the oscillator by two clear rows of
   cells.  The first superfountain was found by Noam Elkies in February
   1998.  In January 2006 Nicolay Beluchenko found the much smaller one
   shown below.  See also {fountain}.
	...........*...........
	.......................
	.......................
	.....*..*.....*..*.....
	...**..*.*****.*..**...
	.....*...........*.....
	...*.**.........**.*...
	.*.*...***...***...*.*.
	***.*.............*.***
	..........*.*..........
	....***...*.*...***....
	....*..*...*...*..*....
	...****..*.*.*..****...
	...**..***.*.***..**...
	..*...*...*.*...*...*..
	...*..*.*.*.*.*.*..*...
	....*.*.**...**.*.*....
	.....*...........*.....

:superlinear growth:  Growth faster than any rate proportional to T,
   where T is the number of ticks that a pattern has been run.  This
   term usually applies to a pattern's population growth, rather than
   diametric growth or bounding-box growth.  For example, {breeder}s'
   and {spacefiller}s' population asymptotically grows faster than any
   linear-growth pattern.  It may also be used to describe the rate of
   increase in the number of subpatterns present in a pattern, such as
   when describing a {replicator}'s rate of reproduction.  Due to limits
   enforced by the {speed of light}, no pattern's population can grow at
   an asymptotic rate faster than {quadratic growth}.  See
   {switch-engine ping-pong} for the lowest-population superlinear
   growth pattern as of July 2018, along with a list of the
   record-holders.

:superstring:  An infinite orthogonal row of cells stabilized on one
   side so that it moves at the {speed of light}, often leaving debris
   behind.  The first examples were found in 1971 by Edward Fitzgerald
   and Robert Wainwright.  Superstrings were studied extensively by
   Peter Rott during 1992-1994, and he found examples with many
   different periods.  (But no odd periods.  In August 1998 Stephen
   Silver proved that odd-period superstrings are impossible.)
     Sometimes a finite section of a superstring can be made to run
   between two tracks ("waveguides").  This gives a {fuse} which can be
   made as wide as desired.  The first example was found by Tony
   Smithurst and uses {tub}s.  (This is shown below.  The superstring
   itself is p4 with a repeating section of width 9 producing one
   blinker per period and was one of those discovered in 1971.  With the
   track in place, however, the period is 8.  This track can also be
   used with a number of other superstrings.)  Shortly after seeing this
   example, in March 1997 Peter Rott found another superstring track
   consisting of {boat}s.  At present these are the only two waveguides
   known.  Both are destroyed by the superstring as it moves along.  It
   would be interesting to find one that remains intact.
     See {titanic toroidal traveler} for another example of a
   superstring.
	.**..........................................................
	*..*...*...*...*...*...*...*...*...*...*...*...*...*...*...*.
	....*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*
	*..*...*...*...*...*...*...*...*...*...*...*...*...*...*...*.
	.***.........................................................
	..**.........................................................
	..**.........................................................
	...*.........................................................
	...*.........................................................
	...*.........................................................
	...*.........................................................
	...*.........................................................
	...*.........................................................
	...*.........................................................
	..**.........................................................
	..**.........................................................
	.***.........................................................
	*..*...*...*...*...*...*...*...*...*...*...*...*...*...*...*.
	....*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*
	*..*...*...*...*...*...*...*...*...*...*...*...*...*...*...*.
	.**..........................................................

:support:  Those parts of an object which are only present in order to
   keep the rest of the object (such an {engine} or an edge {spark})
   working correctly.  These can be components of the object, or else
   accompanying objects used to {perturb} the object.  In many cases
   there is a wide variation of support possible for an engine.  The
   {arm}s in many {puffer}s are an example of support.

:surprise: (p3)  Found by Dave Buckingham, November 1972.
	...*....**
	...***..*.
	.**...*.*.
	*..**.*.**
	.*......*.
	**.*.**..*
	.*.*...**.
	.*..***...
	**....*...

:SW1T43:  A {Herschel-to-glider} converter that produces a
   {tandem glider} useful in the {tee} reaction.  It is classified as a
   "G3" converter because its two gliders are three {lane}s apart.
	.......**........
	.......*.........
	.....*.*.........
	....*.*..........
	**...*...........
	**...............
	...........**....
	...........*.*...
	.............*...
	.............*.**
	..........**.*.**
	*........*..*....
	*.*.......**.....
	***..............
	..*.......****...
	...........*..*..
	.........*...**..
	.........**......
   Besides the southwest-travelling glider on lane 1, the converter also
   emits the Herschel's standard {first natural glider}, {SW-2}.  The
   converter's full standard name is therefore "HSW1T43_SW-2T21".  See
   {NW31} for an explanation of H-to-G naming conventions.

:SW-2:  The simplest type of {H-to-G} {converter}, where the converter's
   effect is simply to suppress a Herschel cleanly after allowing its
   {first natural glider} to escape.  The name should be read as "SW
   minus two", where -2 is a glider {lane} number.  The complete
   designation is SW-2T21.  See {NW31T120} for a discussion of the
   standard naming conventions used for these converters.
     An unlimited number of converters have the SW-2T21 classification.
   The variants most often used consist of just one or two small
   {still life} {catalyst}s.
	...................................**.....
	...................................*......
	.................................*.*......
	.............................**..**.......
	.............................**...........
	.....**...................................
	.....**...................................
	.............................**...........
	.............................**...........
	..........................................
	..........................................
	..........................................
	.........**...............................
	.........**...............................
	..........................................
	*........................*................
	*.*......................*.*..............
	***......................***..............
	..*........................*..............
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	........................................*.
	...........*...........................*.*
	..........*.*...........................**
	..........*.*.............................
	...........*............................**
	*........................*.............*.*
	*.*......................*.*............*.
	***......................***..............
	..*........................*..............

:SW-2T21:  = {SW-2}

:swan: (c/4 diagonally, p4)  A diagonal {spaceship} producing some
   useful sparks.  Found by Tim Coe in February 1996.
	.*..........**..........
	*****......**...........
	*..**........*.......**.
	..**.*.....**......***.*
	...........**...*.**....
	.....*.*......**........
	..........***.*....*....
	.......***...*....*.....
	........*.......*.......
	........*......*........
	........................
	...........*............

:swimmer:  = {switch engine}.

:swimmer lane:  = {switch engine channel}.

:switch:  A {signal}-carrying {circuit} that can send output signals to
   two or more different locations, depending on the state of the
   mechanism.  These may be {toggle circuit}s, where the state of the
   switch changes after each use, or {permanent switch}es that retain
   the same state through many uses until a change is made with a
   separate signal.

     More generally, any circuit may be referred to as a switch, if it
   can alter its output based on stored information.  For example, the
   following simple mechanism based on an eater2 was discovered by
   Emerson J. Perkins in 2007.  It either reflects or absorbs an
   incoming signal, depending on the presence or absence of a nearby
   block.  The block is removed if a reflection occurs.
	...*.....................*....................
	....*...................*.*...................
	..***...................*.*...................
	......................***.**................*.
	..................*..*....................***.
	................***...***.**...**........*....
	...............*........*.**...**........**...
	...............**.............................
	**............................................
	.*............................................
	.*.**.........................................
	..*..*....................................**..
	...**.....................................*.*.
	..................**........................*.
	..................**........................**
	..................................***.........
	..................................*...........
	...................................*..........
	..............................................
	..........................*...**..............
	.........................*.*...*..............
	.....................**.*.*...*...............
	.....................**.*....*................
	.........................*****.*..............
	.................**.*.**.*....**...........***
	.................*.**.*..*.**..............*..
	..........**............**.*.***............*.
	..........**...................*..............
     The switching signal here is a glider produced by a high-clearance
   {syringe} variant found by Matthias Merzenich.  The syringe is not
   technically part of the switch mechanism; any standard {Herschel}
   source can deliver the signal to the block {factory} (the two
   {eater1}s on the right side of the pattern).  Alternate {converter}
   mechanisms could also be used to place the block.
     An earlier example of the same type of one-time switch mechanism,
   also mediated by a block, can be found in the NW34T204 {H-to-G}.  See
   also {bistable switch} for a very robust and versatile toggle switch
   with two input {lane}s and four possible outputs.

:switchable gun:  A {gun} that includes a mechanism to turn the output
   stream off and on with simple signals, often gliders.  A small
   example is Dieter Leithner's switchable LWSS gun from July 8, 1995.
   The ON signal enters from the northeast, and the OFF signal from the
   northwest:
	.................**...........................................
	.................*..*.........................................
	..............................................................
	.....................*........................................
	..............................................................
	.*.................**.........................................
	..*...............*...........................................
	***...........................................................
	..............................................................
	...............**...**........................................
	...............**...**........................................
	................*****........................*................
	.................*.*........................*.................
	............................................***...............
	.................***..........................................
	....................................*.*.......................
	....................................*...*.....................
	........................................*.......*.............
	..........................**........*....*....****............
	..........................**............*....*.*.**...........
	.....................*..............*...*...*..*.***........**
	......................*.............*.*......*.*.**.........**
	....................***.......................****............
	................*...............................*.............
	...............***...................*........................
	..............*****..................*.*.....*................
	.............**...**.................**....***................
	..........................................*...................
	.............................*............**..................
	...........................*..*.........***...................
	...............***..........***.........**....................
	...............***..........*..........*.*....................
	.............................*................................
	.............................***..............................
	................**............................................
	................**............................................
	.....................*........................................
	...................****......**..**...........................
	.............**...*.*.**.....****.*..*.*......................
	.............**..*..*.***.....**.*...*...*....................
	..................*.*.**....*............*.....**.............
	...................****..............*....*....**.............
	.....................*...................*....................
	.....................................*...*....................
	.....................................*.*......................

:switch engine:  The following pattern discovered by Charles Corderman
   in 1971, which is a {glide symmetric} unstable {puffer} which moves
   diagonally at a speed of c/12 (8 cells every 96 generations).
	.*.*..
	*.....
	.*..*.
	...***
     The {exhaust} is {dirty} and unfortunately catches up and destroys
   the switch engine before it runs 13 full periods.  Corderman found
   several ways to stabilize the switch engine to produce {puffer}s,
   using either one or two switch engines in tandem.  See
   {stabilized switch engine} and {ark}.
     No {spaceship}s were able to be made from switch engines until Dean
   Hickerson found the first one in April 1991 (see {Cordership}).
   Switch engine {technology} is now well-advanced, producing many c/12
   diagonal spaceships, puffers, and rakes of many periods.
     Small {polyomino}es exist whose {evolution} results in a switch
   engine. See {nonomino switch engine predecessor}.
     Several three-glider collisions produce {dirty} reactions that
   produce a stabilized switch engine along with other {ash}, making
   {infinite growth}.  Until recently the only known syntheses for
   {clean} unstabilized switch engines used four or more gliders.  There
   are several such recipes.  In the reaction shown below no glider
   arrives from the direction that the switch engine will travel to,
   making it easier to repeat the reaction:
	***................
	..*................
	.*.................
	...................
	.......**..........
	......**...........
	........*..........
	...................
	...................
	...................
	...................
	...................
	...................
	...................
	..**...............
	.*.*...............
	...*...............
	...................
	................***
	................*..
	.................*.
   Running the above for 20 ticks completes a {kickback} reaction with
   the top two gliders, resulting in the three-glider switch engine
   recipe discovered by Luka Okanishi on 12 March 2017.

:switch engine channel:  Two lines of {boat}s (or other suitable
   objects, such as {tub with tail}s) arranged so that a {switch engine}
   can travel between them, in the following manner:
	..............**................
	.............*.*................
	..............*.................
	................................
	................................
	................................
	................................
	................................
	.......***............**........
	........*..*.........*.*........
	............*.........*.........
	.........*.*....................
	................................
	................................
	................................
	................................
	..............................**
	.............................*.*
	..............................*.
	................................
	................................
	.*..............................
	*.*.............................
	**..............................
	................................
	................................
	................................
	................................
	................................
	.........*......................
	........*.*.....................
	........**......................
   David Bell used this in June 2005 to construct a "bobsled"
   oscillator, in which a switch engine {factory} sends switch engines
   down a channel, at the other end of which they are deleted.

:switch engine chute:  = {switch engine channel}

:switch-engine ping-pong:  A very large (210515x183739)
   {quadratic growth} pattern found by Michael Simkin in October 2014.
   Currently this is the smallest starting population (23 cells) known
   to result in a quadratic population growth rate.  Previous
   record-holders include {Jaws}, {mosquito1}, {mosquito2}, {mosquito3},
   {mosquito4}, {mosquito5}, {teeth}, {catacryst}, {metacatacryst},
   {Gotts dots}, {wedge}, {26-cell quadratic growth},
   {25-cell quadratic growth}, and {24-cell quadratic growth}.

:symmetric:  Any object which can be rotated and/or flipped over an axis
   and still maintain the same shape.  Many common small objects such as
   the {block}, {beehive}, {pond}, {loaf}, {clock}, and {blinker} are
   symmetric.  Some larger symmetric objects are {Kok's galaxy},
   {Achim's p16}, {cross}, {Eureka}, and the {pulsar}.
     Large symmetric objects can easily be created by placing multiple
   copies of any finite object together in a symmetrical way.  Unless
   the individual objects interact significantly, this is considered
   trivial and is not considered further here (e.g., two {LWSS}s
   travelling together a hundred cells apart).
     There are two kinds of symmetry.  Odd symmetry occurs when an
   object's line of reflection passes through the center of a line of
   cells.  Objects with odd symmetry have an odd number of columns or
   rows, and can have a {gutter}.  Even symmetry occurs when the line of
   reflection follows the boundary between two lines of cells.  Objects
   with even symmetry have an even number of columns or rows.
     Because the Life universe and its rules are symmetric, all
   symmetric objects must remain symmetric throughout their {evolution}.
   Most non-symmetric objects keep their non-symmetry as they evolve,
   but some can become symmetric, especially if they result in a single
   object.  Here is a slightly more complicated example where two
   gliders interact to form a {blockade}:
	..*.........
	*.*.........
	.**........*
	.........**.
	..........**
     Many useful objects are symmetric along an orthogonal axis.  This
   commonly occurs by placing two copies of an object side by side to
   change the behaviour of the objects due to the inhibition or killing
   of new cells at their {gutter} interface.  Examples of this are
   {twin bees shuttle}, {centinal}, and the object shown in {puffer}.
   Other useful symmetric objects are created by perturbing a symmetric
   object using nearby {oscillator}s or {spaceship}s in a symmetric
   manner.  Examples of this are {Schick engine}, {blinker ship}, and
   {hivenudger}.
     Many {spaceship}s found by {search program}s are symmetric because
   the search space for such objects is much smaller than for
   non-symmetrical spaceships.  Examples include {dart}, {60P5H2V0}, and
   {119P4H1V0}.

:synchronized:  Indicates that precise relative timing is required for
   two or more input {signal}s entering a {circuit}, or two or more sets
   of {glider}s participating in a {glider synthesis}.  Compare
   {asynchronous}.  See also {salvo} and {slow glider construction}.

:synchronous:   = {synchronized}

:synthesis:  = {glider synthesis}

:syringe:  A small stable {converter} found by Tanner Jacobi in March
   2015, accepting a glider as input and producing an output {Herschel}
   As of June 2018 it is the smallest known converter of this type, so
   it is very often used to handle input gliders in complex {signal}
   {circuit}ry, as described in {Herschel circuit}.  A second glider can
   safely follow the first any time after 78 ticks, but {overclocking}
   also allows the syringe to work at a {repeat time} of 74 or 75 ticks.
   If followed by a {dependent conduit} a simple {eater2} can be used
   instead of the large {weld}ed {catalyst} shown here.  A
   {ghost Herschel} marks the output location.
	....*.............................
	.....*............................
	...***............................
	..................*...............
	................***...............
	...............*..................
	...............**.................
	**................................
	.*................................
	.*.**.............................
	..*..*.......................*....
	...**........................*....
	..................**.........***..
	..................**...........*..
	..................................
	..................................
	..................................
	...........................*...**.
	..........................*.*...*.
	.........................*.*...*..
	.....................**.*.*...*...
	.....................**.*..****.*.
	.........................*.*...*.*
	.....................**.**..*..*.*
	......................*.*..**...*.
	..........**..........*.*.........
	..........**...........*..........
     A different version of the large catalyst, with better {clearance}
   for some situations, can be seen in the {switch} entry.

:T:  = {T-tetromino}

:table:  The following {induction coil}.
	****
	*..*

:table on table: (p1)
	*..*
	****
	....
	****
	*..*

:tag:  = {tagalong}

:tagalong:  An object which is not a {spaceship} in its own right, but
   which can be attached to one or more spaceships to form a larger
   spaceship.  For examples see {Canada goose}, {fly}, {pushalong},
   {sidecar} and {sparky}.  See also {Schick engine}, which consists of
   a tagalong attached to two LWSS (or similar).
     The following {c/4 spaceship} (Nicolay Beluchenko, February 2004)
   has two wings, either of which can be considered as a tagalong. But
   if either wing is removed, then the remaining wing becomes an
   essential component of the spaceship, and so is no longer a tagalong.
	.......................*.......................
	.......................*.......................
	......................*.*......................
	...............................................
	.....................*...*.....................
	....................**...**....................
	..................**.*...*.**..................
	................**.*.*...*.*.**................
	............*...***.*.....*.***...*............
	............******...........******............
	...........*..*....*.......*....*..*...........
	...................*.......*...................
	..........***.....................***..........
	.........*.**.....................**.*.........
	........*..*.......................*..*........
	........*.............................*........
	.........**.........................**.........
	.........**.........................**.........
	***......*...........................*......***
	.*......***.........................***......*.
	......**..*.........................*..**......
	..**.*.***...........................***.*.**..
	.*...*.*...............................*.*...*.
	.*...**.................................**...*.

:tail spark:  A {spark} at the back of a spaceship.  For example, the
   1-bit spark at the back of a {LWSS}, {MWSS} or {HWSS} in their less
   dense phases.

:tame:  To {perturb} a {dirty} reaction using other patterns so as to
   make it {clean} and hopefully useful.  Or to make a reaction work
   which would otherwise fail due to unwanted products which interfere
   with the reaction.

:taming:  See {tame}.

:tandem glider:  Two gliders travelling on parallel lanes at a fixed
   spacetime offset, usually as a single signal in a
   {Herschel transceiver}.  See also {glider pair}.

:Tanner's p46: (p46)  An {oscillator} found by Tanner Jacobi on 20
   October 2017.  This oscillator hassles an evolving {pi-heptomino} to
   produce an {phi} {spark}.  The spark is very accessible and is able
   to perturb many things.
	..............*...........
	...**.......**.**.........
	...**.......**.**.....*.**
	......................**.*
	..........................
	..**......................
	...*......................
	***.......................
	*.............*...........
	.............*.*.*.**.....
	............*.**.**.*.....
	............*.............
	...........**.............
   The snakes can be replaced with eaters to form a slightly smaller
   version, as shown in the p46 MWSS gun in {gliderless}
     The period of this new oscillator is the same as the old
   {twin bees shuttle}, and so this is able to expand the known p46
   {technology}.  For example, a p46 glider gun can be made from a
   Tanner's p46 and just one of the {twin bees shuttle}s.
     Acting on their own, two copies of Tanner's p46 placed at right
   angles to each other with their sparks interacting can produce two
   different p46 glider guns and a gliderless p46 MWSS gun.  See
   {p46 gun} and {gliderless} for two of these. These are the first p46
   guns found which do not use a twin bees shuttle at all.

:target:  A necessary component of a {slow salvo} recipe used by a
   {single-arm} {universal constructor}.  A target usually consists of a
   single object, or sometimes a small {constellation} of common still
   lifes and/or oscillators.  See {intermediate target}.  If no {hand}
   target is available, a construction arm may be unable to construct
   anything, unless recipes are available to generate targets directly
   from the {elbow}.

:teardrop:  The following {induction coil}, or the formation of two
   beehives that it evolves into after 20 generations.  (Compare
   {butterfly}, where the beehives are five cells further apart.)
	***.
	*..*
	*..*
	.**.

:technician: (p5)  Found by Dave Buckingham, January 1973.
	.....*.....
	....*.*....
	....**.....
	..**.......
	.*...***...
	*..**...*.*
	.**....*.**
	...*.*.*...
	...*...*...
	....***....
	......*.*..
	.......**..

:technician finished product:  = {technician}

:technology:  The collective set of known reactions exploiting one
   subset of the Life universe.  Examples of these subsets include
   {glider synthesis}, period 30 glider {stream}s, c/3 {spaceship}s,
   {sparker}s, {Herschel conduit}s, and {slow salvo}s.  As new reactions
   and objects are found, over time any particular technology becomes
   more versatile and complete.  Many Life experts like to concentrate
   on particular technologies.

:tee:  A head-on collision between three {glider}s, producing a
   perpendicular output glider that can be used to construct closely
   spaced glider {salvo}s, or to {inject} a glider into an existing
   {stream}.  There are several workable {recipe}s.  One of the more
   useful is the following, because the {tandem glider} can be generated
   by a small {Herschel} {converter}, {SW1T43}:
	...............*.
	..............*..
	..............***
	.........*.......
	.........*.*.....
	.........**......
	.**..............
	*.*..............
	..*..............

:teeth:  A 65-cell quadratic growth pattern found by Nick Gotts in March
   2000.  This (and a related 65-cell pattern which Gotts found at about
   the same time) beat the record previously held by {mosquito5} for
   smallest population known to have superlinear growth, but was later
   superseded by {catacryst}.  See {switch-engine ping-pong} for the
   lowest-population {superlinear growth} pattern as of July 2018, along
   with a list of the record-holders.

:telegraph:  A pattern created by Jason Summers in February 2003.  It
   transmits and receives information using a rare type of
   {reburnable fuse}, a {lightspeed wire} made from a chain of beehives,
   at the rate of 1440 ticks per bit.  The rate of travel of signals
   through the entire {transceiver} device can be increased to any speed
   strictly less than the {speed of light} by increasing the length of
   the beehive chain appropriately.
     "Telegraph" may also refer to any device that sends and receives
   lightspeed signals; see also {p1 telegraph},
   {high-bandwidth telegraph}.

:ternary reaction:  Any reaction between three objects.  In particular,
   a reaction in which two gliders from one stream and one glider from a
   crossing stream of the same period annihilate each other.  This can
   be used to combine two glider guns of the same period to produce a
   new glider gun with double the period.

:test tube baby: (p2)
	**....**
	*.*..*.*
	..*..*..
	..*..*..
	...**...

:tetraplet:  Any 4-cell {polyplet}.

:tetromino:  Any 4-cell {polyomino}.  There are five such objects, shown
   below.  The first is the {block}, the second is the {T-tetromino} and
   the remaining three rapidly evolve into {beehive}s.
	**......***......****......***......**.
	**.......*...................*.......**

:The Online Life-Like CA Soup Search:  A distributed search effort set
   up by Nathaniel Johnston in 2009, using a Python script running in
   {Golly}.  Results included a collection of the longest-lived 20x20
   soups, as well as a {census} of over 174 billion {ash} objects.  It
   has since been superseded by {Catagolue}.

:The Recursive Universe:  A popular science book by William Poundstone
   (1985) dealing with the nature of the universe, illuminated by
   parallels with the game of Life.  This book brought to a wider
   audience many of the results that first appeared in {LifeLine}.  It
   also outlines the proof of the existence of a {universal constructor}
   in Life first given in {Winning Ways}.

:thumb:  A {spark}-like protrusion which flicks out in a manner
   resembling a thumb being flicked.  Below on the left is a p9 thumb
   sparker found by Dean Hickerson in October 1998.  On the right is a
   p4 example found by David Eppstein in June 2000.
	.......*..............*.....
	...**...*.........**...*....
	...*.....*.**.....*.....*...
	**.*.*......*......***.*.**.
	**.*.**.****............**.*
	...*.*...........******....*
	...*.*.***.......*....*****.
	....*.*...*.........*.......
	......*..**........*.****...
	......**...........*.*..*...
	....................*.......

:thunderbird: (stabilizes at time 243)
	***
	...
	.*.
	.*.
	.*.

:tick:  = {generation}

:tic tac toe:  = {octagon II}

:tie:  A term used in naming certain {still life}s (and the {stator}
   part of certain {oscillator}s).  It indicates that the object
   consists of two smaller objects joined point to point, as in
   {ship tie boat}.

:time bomb:  The following pattern by Doug Petrie, which is really just
   a glider-producing {switch engine} in disguise.  See
   {infinite growth} for some better examples of a similar nature.
	.*...........**
	*.*....*......*
	.......*....*..
	..*..*...*..*..
	..**......*....
	...*...........

:titanic toroidal traveler:  The {superstring} with the following
   repeating segment.  The front part becomes p16, but the eventual fate
   of the detached back part is unknown.
	******
	***...

:TL:  = {traffic light}

:T-nosed p4: (p4)  Found by Robert Wainwright in October 1989.  See also
   {filter}.
	.....*.....
	.....*.....
	....***....
	...........
	...........
	...........
	...*****...
	..*.***.*..
	..*.*.*.*..
	.**.*.*.**.
	*..**.**..*
	**.......**

:T-nosed p5: (p5)  Found by Nicolay Beluchenko in April 2005.
	.....**...............**.**.....*........
	..*..*.........**.*.***.**......*........
	.*.*.*.....*....*.*.***......**.*........
	*..*.*.******.....*....*.*...**.*........
	.**.*.*..*...***..*.****..*.*.**.**......
	..*.*..**.*..*..*.**....***.*.*....**....
	.*..*...*..*.*.**....***...*.............
	.*.*.*...***.*...****...*..*.*..**.*..*..
	**.*.........**.*....*.*.*.*........*.***
	.*.*.*...***.*...****...*..*.*..**.*..*..
	.*..*...*..*.*.**....***...*.............
	..*.*..**.*..*..*.**....***.*.*....**....
	.**.*.*..*...***..*.****..*.*.**.**......
	*..*.*.******.....*....*.*...**.*........
	.*.*.*.....*....*.*.***......**.*........
	..*..*.........**.*.***.**......*........
	.....**...............**.**.....*........

:T-nosed p6: (p6)  Found by Achim Flammenkamp in September 1994. There
   is also a much larger and fully symmetric version found by
   Flammenkamp in August 1994.
	......**...**......
	......*.*.*.*......
	.......*...*.......
	...................
	..*.*.*.....*.*.*..
	***.*.**...**.*.***
	..*.*.*.....*.*.*..
	...................
	.......*...*.......
	......*.*.*.*......
	......**...**......

:toad: (p2)  Found by Simon Norton, May 1970.  This is the second most
   common {oscillator}, although {blinker}s are more than a hundred
   times as frequent.  See also {killer toads}.  A toad can be used as a
   90-degree {one-time} {turner}.
	.***
	***.
     The protruding cells at the edges can perturb some reactions by
   encouraging and then suppressing births on successive ticks.  For
   example, a toad can replace the northwest eater in the
   {Callahan G-to-H} converter, allowing it to be packed one diagonal
   cell closer to other circuits.

:toad-flipper:  A {toad} {hassler} that works in the manner of the
   following example.  Two {domino} {sparker}s, here {pentadecathlon}s,
   apply their {spark}s to the toad in order to flip it over.  When the
   sparks are applied again it is flipped back.  Either or both domino
   sparkers can be moved down two spaces from the position shown and the
   toad-flipper will still work, but because of symmetry there are
   really only two different types.  Compare {toad-sucker}.
	.*..............*.
	.*..............*.
	*.*............*.*
	.*..............*.
	.*......*.......*.
	.*......**......*.
	.*......**......*.
	*.*......*.....*.*
	.*..............*.
	.*..............*.

:toad-sucker:  A {toad} {hassler} that works in the manner of the
   following example.  Two {domino} {sparker}s, here {pentadecathlon}s,
   apply their {spark}s to the toad in order to shift it.  When the
   sparks are applied again it is shifted back.  Either or both domino
   sparkers can be moved down two spaces from the position shown and the
   toad-sucker will still work, but because of symmetry there are really
   only three different types.  Compare {toad-flipper}.
	.*................
	.*..............*.
	*.*.............*.
	.*.............*.*
	.*......*.......*.
	.*......**......*.
	.*......**......*.
	*.*......*......*.
	.*.............*.*
	.*..............*.
	................*.

:toaster: (p5)  Found by Dean Hickerson, April 1992.
	....*......**..
	...*.*.**..*...
	...*.*.*.*.*...
	..**.*...*.**..
	*...**.*.**...*
	...*.......*...
	...*.......*...
	*...**.*.**...*
	..**.*...*.**..
	...*.*.*.*.*...
	...*.*.**..*...
	....*......**..

:toggleable gun:  Any {gun} that can be turned off or turned on by the
   same external signal - the simplest possible switching mechanism.  An
   input signal causes the gun to stop producing gliders.  Another input
   signal from the same source restores the gun to its original
   function.  Compare {switchable gun}.
     Here's a small example by Dean Hickerson from September 1996:
	..............**..............*..
	..............*.*.............*.*
	..............*...............**.
	.................................
	.................................
	.................................
	.................................
	...............*..*....b.........
	.****..............*..b..........
	*...*..........*...*..bbb........
	....*...........****.............
	*..*........................aaa..
	............................a....
	.............................a...
   In the figure above, glider B and an LWSS are about to send a glider
   NW.  Glider A will delete the next glider after B, turning off the
   output stream.  But if the device were already off, B wouldn't be
   present and A would instead delete the leading LWSS, turning the
   device back on.

:toggle circuit:  Any signal-processing {circuit} that switches back and
   forth between two possible states or outputs.  An early example is
   the {boat-bit}.  More recent discoveries include the {semi-Snark}s,
   which alternate between reflecting and absorbing input {glider}s.
   The following B-to-G {converter} sends alternate glider outputs in
   opposite directions.
	...........**....................................**....
	......**..*.*...............................**..*.*....
	......*...*....*............................*...*....*.
	.......***.*****.............................***.*****.
	.........*.*...................................*.*.....
	.........*.*.***...............................*.*.***.
	..........**.*..*...............................**.*..*
	...............**....................................**
	.......................................................
	.......................................................
	.............................................**........
	.............................................**........
	.......................................................
	.......................................................
	.......................................................
	**....................................**...............
	**....................................**...............
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.........**....................................**......
	.........**....................................**......
	.......................................................
	**.*.......*..........................**.*.......*.....
	*.**......***.........................*.**......***....
	.........**..*.................................**..*...

:TOLLCASS:  Acronym for {The Online Life-Like CA Soup Search}.

:toolkit:  A set of Life reactions and mechanisms that can be used to
   solve any problem in a specific pre-defined class of problems:
   {glider} timing adjustment, {salvo} creation, {seed} construction,
   etc.  See also {universal toolkit}, {technology}.

:torus:  As applies to Life, usually means a finite Life universe which
   takes the form of an m x n rectangle with the bottom edge considered
   to be joined to the top edge and the left edge joined to the right
   edge, so that the universe is topologically a torus. There are also
   other less obvious ways of obtaining a toroidal universe.
     See also {Klein bottle}.  Every object in a torus universe
   obviously either dies or becomes a {still life} or {oscillator}.

:total aperiodic:  Any finite pattern which evolves in such a way that
   no cell in the Life plane is eventually periodic.  The first example
   was found by Bill Gosper in November 1997.  A few days later he found
   the following much smaller example consisting of three copies of a
   p12 {backrake} by Dave Buckingham.
	.........................................*.................
	........................................***................
	.......................................**.*.....*..........
	.......................................***.....***.........
	........................................**....*..**...***..
	..............................................***....*..*..
	........................................................*..
	........................................................*..
	........................................................*..
	........................................***............*...
	........................................*..*...............
	........................................*..................
	........................................*..................
	.........................................*.................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	......................................***..................
	......................................*..*...........*.....
	......................................*.............***....
	......................................*............**.*....
	......................................*............***.....
	.......................................*............**.....
	...........................................................
	...........................................................
	...................................***.....................
	..................................*****....................
	..................................***.**.......**........*.
	.....................................**.......****........*
	..............................................**.**...*...*
	................................................**.....****
	...........................................................
	...........................................................
	....................*......................................
	.....................*.....................................
	.**.............*....*................................***..
	****.............*****..................................*..
	**.**...................................................*..
	..**...................................................*...
	....................................*......................
	.....................................*.....................
	.....................**..........*...*.....................
	......................**..........****...............**....
	.....................**...........................***.**...
	.....................*............................*****....
	...................................................***.....
	...........................................................
	......................**...................................
	.............****....****..................................
	............*...*....**.**.................................
	.*****..........*......**..................................
	*....*.........*...........................................
	.....*.....................................................
	....*......................................................

:T-pentomino:  Conway's name for the following {pentomino}, which is a
   common {parent} of the {T-tetromino}.
	***
	.*.
	.*.

:track:  A path made out of {conduit}s, often ending where it begins so
   that the active {signal} object is cycled forever, forming an
   {oscillator} or a {gun}.
     This term has also been used to refer to the {lane} on which a
   {glider} or {spaceship} travels.  The concept is very similar, but a
   reference to a "track" now usually implies a non-trivial supporting
   conduit.

:tractor beam:  A stream of {spaceship}s that can draw an object towards
   the source of the stream.  The example below shows a tractor beam
   pulling a {loaf}; this was used by Dean Hickerson to construct a
   {sawtooth}.
	.....................*..*......................
	.....****...........*..............****........
	.....*...*..........*...*..........*...*.......
	.....*........**....****...........*........**.
	.**...*..*...****...........**......*..*...****
	*..*........**.**..........**.**..........**.**
	*.*..........**.............****...........**..
	.*...........................**................

:traffic circle: (p100)
	.....................**....**...................
	.....................*.*..*.*...................
	.......................*..*.....................
	......................**..**....................
	.....................***..***...................
	.......................*..*.....................
	...............................*................
	..............................*.**..............
	..................................*.............
	..........................*...*..*.*............
	..........................*.....*..*............
	..........................*......**.............
	.........**.....................................
	........*..*..........***...***.................
	.......*.*.*....................................
	......***.*...............*.....................
	......***.................*.....................
	..........................*.....................
	............***.................................
	**..*................***........................
	*..**.....*.....*...............................
	.*****....*.....*..*.....*.................*..**
	..........*.....*..*.....*.................**..*
	...................*.....*.......***......*****.
	.*****......***.................................
	*..**................***.......*.....*..........
	**..*..........................*.....*....*****.
	...............................*.....*.....**..*
	...........................................*..**
	.................................***............
	.......................................**.......
	......................................***.......
	.....................................*.**.......
	....................................*.*.........
	....................***.............*..*........
	.....................................**.........
	.............**....*..*.........................
	............*..*................................
	............*.*.*...............................
	.............*..*...............................
	.................*..............................
	..............*.*...............................
	.....................*..*.......................
	...................***..***.....................
	....................**..**......................
	.....................*..*.......................
	...................*.*..*.*.....................
	...................**....**.....................

:traffic jam:  Any {traffic light} {hassler}, such as {traffic circle}.
   The term is also applied to the following reaction, used in most
   traffic light hasslers, in which two traffic lights interact in such
   a way as to reappear after 25 generations with an extra 6 spaces
   between them.   See {traffic lights extruder} for a way to make this
   reaction {extensible}.
	..***...........
	...........***..
	*.....*.........
	*.....*..*.....*
	*.....*..*.....*
	.........*.....*
	..***...........
	...........***..

:traffic light: (p2)  A common formation of four blinkers.
	..***..
	.......
	*.....*
	*.....*
	*.....*
	.......
	..***..

:traffic lights extruder:  A growing pattern constructed by Jason
   Summers in October 2006, which slowly creates an outward-growing
   chain of {traffic light}s.  The growth occurs in waves which travel
   through the chain from one end to the other.  It can be thought of as
   a complex {fencepost} for a {wick} that does not need a
   {wickstretcher}.
     The following illustrates the reaction used, in which a newly
   created traffic light at the left eventually pushes the rightmost one
   slightly to the right.
	......................*.......................*....
	......................*.......................*....
	.........***..........*..........***..........*....
	.**................................................
	***....*.....*....***...***....*.....*....***...***
	.**....*.....*.................*.....*.............
	.......*.....*........*........*.....*........*....
	......................*.......................*....
	.........***..........*..........***..........*....

:trans-beacon on table: (p2)
	....**
	.....*
	..*...
	..**..
	......
	****..
	*..*..

:trans-boat with tail: (p1)
	**...
	*.*..
	.*.*.
	...*.
	...**

:transceiver:  = {Herschel transceiver}.

:trans-loaf with tail: (p1)
	.*....
	*.*...
	*..*..
	.**.*.
	....*.
	....**

:transmitter:  = {Herschel transmitter}.

:transparent:  In signal circuitry, a term used for a {catalyst} that is
   completely destroyed by the passing signal, then rebuilt.  Often
   (though not always) the active reaction passes directly through the
   area occupied by the transparent catalyst, then rebuilds the catalyst
   behind itself, as in the {transparent block reaction}.  See also
   {transparent lane}.

:transparent block reaction:  A certain reaction between a block and a
   {Herschel} {predecessor} in which the block reappears in its original
   place some time later, the reaction having effectively passed through
   it.  This reaction was found by Dave Buckingham in 1988.  It has been
   used in some {Herschel conduit}s, and in the {gunstar}s.  Because the
   reaction involves a Herschel predecessor rather than an actual
   Herschel, the following diagram shows instead a {B-heptomino} (which
   by itself would evolve into a block and a Herschel).
	*.............
	**..........**
	.**.........**
	**............

:transparent debris effect:  A mechanism where a {Herschel} or other
   active reaction completely destroys a {catalyst} in a particular
   location in a {conduit}.  After passing through or past that
   location, the same reaction then recreates the catalyst in exactly
   its original position.  This type of catalysis is surprisingly common
   in {signal} {circuit}ry.  For an example, see
   {transparent block reaction}.
     The transparent object is most often a very common {still life}
   such as a block or beehive.  Rarer objects are not unknown; for
   example, a transparent {loaf} was found by Stephen Silver in October
   1997, in a very useful {elementary conduit} making up part of a
   {Herschel receiver}.  However, not surprisingly, rarer objects are
   much less likely to reappear in exactly the correct location and
   orientation, so transparent reactions involving them are much more
   difficult to find, on average.

:transparent lane:  A path through a signal-producing {circuit} that can
   be used to merge signal streams.  The signal is usually a
   {standard spaceship} such as a {glider}.  It can either be produced
   by the circuit, or it can come from elsewhere, passing safely through
   on the same {lane} without interacting with the circuit.  A good
   example is the NW31 converter, which has two glider outputs on
   transparent lanes:
	**.......................
	.*.......................
	.*.*.....................
	..**.....................
	.........................
	.........................
	.........................
	.......................**
	.......................**
	.........................
	..*......................
	..*.*....................
	..***....................
	....*....................
	.........................
	.........................
	.........................
	.........................
	.........................
	.........................
	.........................
	.........................
	.............**..........
	.............**..........
     The optional third output shown in {NW31} is non-transparent,
   because the upper {eater1} catalyst would get in the way of a passing
   glider on the same lane.

:tremi-Snark:  A {colour-preserving} period-multiplying {signal}
   {conduit} found by Tanner Jacobi on 7 September 2017, producing one
   output {glider} for every three input gliders.  It uses the same
   block-to-pre-honeyfarm {bait} reaction as the {Snark}, and so has the
   same 43-{tick} {recovery time}.  Compare {semi-Snark}.
	.*............................
	..*...........................
	***...........................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	...........*..................
	............**................
	...........**.................
	..............................
	...........................*..
	.........................***..
	........................*.....
	........................**....
	..............................
	..............................
	..............................
	.......................*......
	.....................*.*......
	......................**......
	..............**..............
	.............*.*........*.....
	.............*.........*.*....
	............**.........*.*....
	........................*.....
	..............................
	..............................
	..............................
	.....................**.**....
	.................**..**.*...**
	.................*......*.*..*
	..................*******.**..
	.........................*....
	....................****.*....
	....................*..**.....

:trice tongs: (p3)  Found by Robert Wainwright, February 1982.  In terms
   of its 7x7 {bounding box} this ties with {jam} as the smallest p3
   {oscillator}.
	..*....
	..***..
	**...*.
	.*.*.*.
	.*.....
	..**..*
	.....**

:trigger:  A {signal}, usually a single {glider}, that collides with a
   {seed} {constellation} to produce a relatively rare still life or
   oscillator, or an output {spaceship} or other signal.  The
   constellation is destroyed or damaged in the process; compare
   {circuit}, {reflector}.  Here a pair of trigger gliders strike a
   {dirty} seed constellation assembled by Chris Cain in March 2015, to
   launch a three-engine {Cordership}:
	....................................................**.
	................................................**..**.
	................................................**.....
	.......................................................
	.......................................................
	.......................................................
	........................................**.............
	........................................**.............
	...................................................**..
	..................................*................*.*.
	.................................*.*...........**...*.*
	..................................**..........*.*....*.
	...............................................*.......
	.......................................................
	..................................*.................***
	.................................*.*................*..
	..................................**.................*.
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	...........................*...........................
	..........................*.*..........................
	...........................**..........................
	.......................................................
	.......................................................
	...........................*...........................
	..........................*.*..........................
	...........................**..........................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......*....*..........................................
	......*.*..*.*.........................................
	.......**...**.........................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	**.....................................................
	*.*....................................................
	.*.*...................................................
	..*....................................................
	.......................................................
	.......................................................
	.......................................................
	.............*.........................................
	............**.........................................
	............*.*........................................
     "Trigger" is also used when a spaceship reacts with another object
   to cause a reaction to occur whenever desired (but perhaps only at
   particular intervals).  The object being triggered lies {dormant}
   until the reaction is required.  All {turner}s and {freeze-dried}
   constellations are triggerable.
     In some cases the object is not destroyed so that the reaction can
   be repeated after some {repeat time}.  See for example {converter}
   and {reflector}, and more specifically {MWSS out of the blue} and
   {queen bee shuttle pair}.

:triomino:  Either of the two 3-cell {polyomino}es.  The term is rarely
   used in Life, since the two objects in question are simply the
   {blinker} and the {pre-block}.

:triple caterer: (p3)  Found by Dean Hickerson, October 1989.  Compare
   {caterer} and {double caterer}.
	.....**.........
	....*..*..**....
	....**.*...*....
	......*.***....*
	..***.*.*....***
	.*..*..*....*...
	*.*..*...*..**..
	.*..............
	..**.**.**.**...
	...*...*...*....
	...*...*...*....

:triple pseudo:  The following pattern, found by Gabriel Nivasch in July
   2001.  It is unique among 32-bit {still life}s in that it can be
   broken down into three {stable} pieces but not into two.  The term
   may also refer to any larger {stable} pattern with the same property.
   See also {quad pseudo}.
	......**
	..*.*..*
	.*.**.*.
	.*....**
	**.**...
	...**.**
	**....*.
	.*.**.*.
	*..*.*..
	**......

:triplet:  Any 3-cell {polyplet}.  There are 5 such objects, shown
   below.  The first two are the two {triomino}es, and the other three
   vanish in two generations.
	*..................*.......*.......*..
	**......***......**.......*.*.......*.
	.....................................*

:tripole: (p2)  The {barberpole} of length 3.
	**....
	*.*...
	......
	..*.*.
	.....*
	....**

:tritoad: (p3)  Found by Dave Buckingham, October 1977.
	.........**.......
	.........*........
	..........*..**...
	.......***.*..*...
	......*....**.*.**
	......*.**..*.*.**
	...**.*...**..*...
	...*..**...*.**...
	**.*.*..**.*......
	**.*.**....*......
	...*..*.***.......
	...**..*..........
	........*.........
	.......**.........

:trivial:  A trivial period-N oscillator is one in which every cell
   oscillates at some smaller factor of N.  See {omniperiodic}.  For
   example, the joining of a period 3 and a period 4 {oscillator} as
   shown below creates a single object which is a trivial oscillator of
   period 12.
	........*.*.
	...........*
	.......*..*.
	......*.*.*.
	......*..*..
	....**.**...
	...*..*.....
	....*.*.....
	**...*......
	.*.**.......
	...*........
	...*........
   However, there are trivial oscillators that meet this requirement,
   but may still be considered to be {non-trivial} because the
   different-period {rotor}s are not separated by {stator} cells.  An
   example is Dean Hickerson's {trivial p6}.  Conversely, there are
   oscillators formed by trivial combinations of high-period {gun}s or
   {sparker}s that are only technically non-trivial, because the
   lower-period components overlap but do not interact in any way.
     "Trivial" is also used to describe a {parent} of an object which
   has groups of cells that can be removed without changing the result,
   such as isolated faraway cells.  For example, here is a trivial
   parent of a block.
	*......
	.*....*
	.*.....
	*......

:trivial p6: (p6)  An {oscillator} found by Dean Hickerson in December
   1994. Every cell has period less than 6, so this is a {trivial}
   oscillator. It is unusual because it has period-2 cells in contact
   with period-3 cells.
	...........**..............
	...........*......**.......
	........**.*......*..*.....
	........*.*.**.**.*.**..*..
	.*........*..*.*..*..*.*.*.
	.*.*.....**..*.*.*.**..*..*
	.*.*.*........**.*.*.**.**.
	.......*.*.***...*....**...
	..*...*....*.**........*...
	....*...***..**.***.*.*.**.
	**..*......*..........*.*..
	..*...........**.**...*.*..
	........*.*****...*....*...
	........**...*..*..*.......
	...........****.***........
	........***....*...........
	........*..*..*..**........
	..........**...**.*........

:trombone slide:  An arrangement of four 90-degree {reflector}s that can
   be placed into the path of a {glider} so as to delay it by an
   adjustable number of generations, without changing its {lane}.  More
   generally, any combination of {circuit}s may be referred to as a
   trombone slide, if the grouping can be moved as a single unit that
   functions as a 180-degree glider {reflector}.
     The smallest known trombone slides are made using {Snark}s.  In the
   trombone slide shown below, sample input and output gliders are
   shown.  The input glider will reach the same output location 128
   generations sooner if the trombone slide is removed.
     If the top and left Snarks are moved together diagonally to the
   upper left by N cells, then the glider delay is increased by 8N
   generations since the glider has to travel N more cells in each
   direction.  This sliding action gives the trombone slide its name.
   If only the final Snark is moved, then the output glider's path can
   be altered by a number of full diagonals.
	......................**...**....................
	......................**..*.***..................
	..........................*....*.................
	......................****.**..*.................
	......................*..*.*.*.**................
	.........................*.*.*.*.................
	..........................**.*.*.................
	..............................*..................
	.................................................
	................**...............................
	.................*.......**......................
	.................*.*.....**......................
	..................**.............................
	.................................................
	.................................................
	.............................................*...
	...........................................***...
	..........................................*......
	..........................................**.....
	............................**...................
	............................*....................
	.............................***..............***
	...............................*................*
	...............................................*.
	.................................................
	................................**...............
	....*..........................*.*.....**........
	..*****..............**........*.......**........
	.*.....*.............*........**.................
	.*..***............*.*...........................
	**.*...............**.......................*....
	*..****.................................**.*.*...
	.**...*...**...........................*.*.*.*...
	...***....**........................*..*.*.*.**..
	...*................................****.**..*...
	**.*....................................*....*...
	**.**...............................**..*.***....
	....................................**...**......
	.................................................
	...........**....................................
	............*....................*...............
	.........***...**..............*****.............
	.........*......*.............*.....*............
	................*.*............***..*............
	.................**...............*.**...........
	...............................****..*...........
	..........................**...*...**............
	..........................**....***..............
	..................................*..............
	..................................*.**...........
	.................................**.**...........
	.................................................
	.................................................
	..............***........**......................
	................*........*.......................
	...............*..........***....................
	............................*....................
     Trombone slides made of the same type of component cannot alter the
   glider path by half-diagonals, and can only change the timing by
   multiples of 8 generations.  For other timing changes, different
   components are necessary.  These may be stable like the
   {Silver reflector} or the {colour-changing} example shown in the
   {reflector} article, or periodic like the various {bumper}s.

:true:  Opposite of {pseudo}.  A {gun} emitting a period n stream of
   {spaceship}s (or {rake}s) is said to be a true period n gun if its
   mechanism oscillates with period n.  The same distinction between
   true and pseudo also exists for {puffer}s.  An easy way to check that
   a gun is true period n is to stop the output with an {eater}, and
   check that the result is a period-n {oscillator}.
     True period n guns are known to exist for all periods greater than
   61 (see {My Experience with B-heptominos in Oscillators}), but only a
   few smaller periods have been achieved, namely 20, 22, 24, 30, 36,
   40, 44, 45, 46, 48, 50, and 54 through 61.  See also {Quetzal} for
   the 54-61 range.
	------------------------------------
	Period  Discoverers            Date
	------------------------------------
	20      Matthias Merzenich  May 2013
	        Noam Elkies
	22      David Eppstein      Aug 2000
	        Jason Summers
	24      Noam Elkies         Jun 1997
	30      Bill Gosper         Nov 1970
	36      Jason Summers       Jul 2004
	40      Adam P. Goucher     Mar 2013
	        Matthias Merzenich
	        Jason Summers
	44      Dave Buckingham     Apr 1992
	45      Matthias Merzenich  Apr 2010
	46      Bill Gosper             1971
	48      Noam Elkies         Jun 1997
	50      Dean Hickerson      Oct 1996
	        Noam Elkies
	        Dave Buckingham
	54      Dieter Leithner     Jan 1998
	        Noam Elkies
	        Dave Buckingham
	55      Stephen Silver      Oct 1998
	56      Dieter Leithner     Jan 1998
	        Dave Buckingham
	        Noam Elkies
	57      Matthias Merzenich  Apr 2016
	58      'thunk'             Apr 2016
	        Matthias Merzenich
	        Chris Cain
	59      Adam P. Goucher     Dec 2009
	        Jason Summers
	60      Bill Gosper         Nov 1970
	61      Luka Okanishi       Apr 2016
	------------------------------------

:T-tetromino:  The following common {predecessor} of a {traffic light}.
	***
	.*.

:tub: (p1)
	.*.
	*.*
	.*.

:tubber: (p3)  Found by Robert Wainwright before June 1972.
	....*.*......
	....**.*.....
	.......***...
	....**....*..
	**.*..**..*..
	.*.*....*.**.
	*...*...*...*
	.**.*....*.*.
	..*..**..*.**
	..*....**....
	...***.......
	.....*.**....
	......*.*....

:tubeater:  A pattern that consumes the output of a {tubstretcher}. The
   smallest known tubeater was found by Nicolay Beluchenko (September
   2005), and is shown below in conjunction with the smallest known
   tubstretcher.
	........*....................
	.......**....................
	.......*.*...................
	.............................
	..........**.................
	..........**.................
	.......................***...
	.*......**...*.........*.....
	**.....*..*.*.*.........*....
	*.*...**.*...*.*..........***
	....*.........*.*............
	...*...........*.*.....**....
	...*..*.........*.*....*.*.*.
	.................*.*...*...**
	..................*.....*....
	...................*..**..*..
	.....................*.****..
	......................***...*
	..........................**.
	...........................*.
	...........................**
	..........................*..
	...........................**

:tubstretcher:  Any {wickstretcher} in which the wick is two diagonal
   lines of cells forming, successively, a {tub}, a {barge}, a
   {long barge}, etc.  The first one was found by Hartmut Holzwart in
   June 1993, although at the time this was considered to be a
   boatstretcher (as it was shown with an extra cell, making the tub
   into a {boat}).  The following small example is by Nicolay Beluchenko
   (August 2005), using a {quarter}.
	.......***.....
	.......*.......
	........*......
	..........**...
	...........*...
	...............
	........**...*.
	***.....**..*.*
	*......*.*...*.
	.*....**.......
	...****.*......
	....**.........
     In October 2005, David Bell constructed an adjustable high-period
   diagonal c/4 {rake} that {burn}s tubstretcher wicks to create
   {glider}s, which are then turned and duplicated by {convoy}s of
   diagonal {c/4 spaceship}s to re-ignite the stabilized ends of the
   same wicks.

:tub with tail: (p1)  The following 8-cell {still life}.  See {eater}
   for a use of this object.
	.*...
	*.*..
	.*.*.
	...*.
	...**

:tugalong:  = {tagalong}

:tumbler: (p14)  The smallest known p14 {oscillator}.  Found by George
   Collins in 1970.  The oscillator generates {domino} {spark}s, but
   they are fragile and no use has been found for them to date.  In each
   domino, one cell is "held" (remains alive) for two generations, the
   other for three.  By contrast, useful domino sparks are usually alive
   for only one tick per oscillator {period}.
	.*.....*.
	*.*...*.*
	*..*.*..*
	..*...*..
	..**.**..

:tumbling T-tetson: (p8)  A {T-tetromino} {hassle}d by two {figure-8}s.
   Found by Robert Wainwright.
	.***.................
	*..................**
	*...*............*.**
	*..*.*..........*....
	..*.*..*...........*.
	...*...*.......**.*..
	.......*.......**....
	....***....*.........
	.........**..........
	...........*.........

:Turing machine:  See {universal computer}.

:turner:  A {one-time} {glider} {reflector}, or in other words a
   single-glider {seed} (the term is seldom or never used in relation to
   spaceships other than gliders).  One-time turners may be 90-degree or
   180-degree, or they may be 0-degree with the output in the same
   direction as the input.  A reusable turner would instead be called a
   reflector.  Shown on the top row below are the four 90-degree turner
   reactions that use common small {ash} objects:  {boat}, {eater1},
   {long boat}, and {toad}.
	.*..............*..............*..............*.........
	..*..............*..............*..............*........
	***............***............***............***........
	........................................................
	........................................................
	........................................................
	.....**........**...............*.......................
	....*.*.......*.*..............*.*...............***....
	.....*........*.................*.*...............***...
	.............**..................**.....................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	.*..............*..............*..............*.........
	..*..............*..............*....**........*........
	***............***............***....**......***........
	......................................................**
	......................................................**
	........................................................
	...*...............**...................................
	..*.*.............*.*............**..............**.....
	.*.*.............*.*.............**..............**.....
	.**..............**.....................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	.*......................................................
	..*.....................................................
	***.....................................................
	........................................................
	........................................................
	........................................................
	....**..................................................
	..*..*..................................................
	..**....................................................
     Of the reactions on the first row, the glider output is the same
   {parity} for all but the long boat. The three still lifes are all
   {colour-changing}, but the {toad} happens to be a {colour-preserving}
   turner.  The third row shows an {aircraft carrier} serving as a
   "0-degree turner" that is also colour-changing.
     Three of the simplest 180-degree turners are shown in the second
   row. The {Blockic} 180-degree turner is colour-preserving. The
   {long boat} and {long ship} are again colour-changing; this is
   somewhat counterintuitive as the output glider is on exactly the same
   {lane} as the input glider, but gliders travelling in opposite
   directions on the same lane always have opposite colours.
     Many small one-time turner {constellation}s have also been
   catalogued. The 90-degree two-block turner on the right, directly
   below the toad, is also colour-changing but has the opposite parity.
     A one-time turner reaction can be used as part of a glider
   {inject}ion mechanism, or as a switching mechanism for a {signal}.
   If a previous reaction has created the sacrificial object, then a
   later glider is turned onto a new path.  Otherwise it passes through
   the area unaffected.  This is one way to create simple switching
   systems or logic {circuit}s.  An example is shown in {demultiplexer}.

:turning toads: (p4 wick)  Found by Dean Hickerson, October 1989.
	..............**.....**.....**.....**.....**..............
	.......*.....*......*......*......*......*................
	......**...*....*.*....*.*....*.*....*.*....*.*.*.**......
	..**.*.***.*..**..*..**..*..**..*..**..*..**..*..*..*.**..
	*..*.**.........................................*****.*..*
	**.*..............................................**..*.**
	...*..................................................*...
	...**................................................**...

:turtle: (c/3 orthogonally, p3)  A {spaceship} found by Dean Hickerson
   in August 1989 that produces a {domino} {spark} at the back.
   Hickerson used this spark to convert an approaching {HWSS} into a
   {loaf}, as part of the first {sawtooth}.  (Also see {tractor beam}).
   The shape of the back end of the turtle is distinctive.  Very similar
   but wider back ends have been found in other c/3 ships to produce
   period 9 and 15 {spaceship}s.
	.***.......*
	.**..*.**.**
	...***....*.
	.*..*.*...*.
	*....*....*.
	*....*....*.
	.*..*.*...*.
	...***....*.
	.**..*.**.**
	.***.......*

:twin bees shuttle: (p46)  Found by Bill Gosper in 1971, this was the
   basis of all known {true} p46 {gun}s, and all known p46 oscillators
   except for {glider} {signal} loops using {Snark}s, until the
   discovery of {Tanner's p46} in 2017.  See {new gun} for an example.
   There are numerous ways to stabilize the ends, two of which are shown
   in the diagram.  On the left is David Bell's {double block reaction}
   (which results in a shorter, but wider, shuttle than usual), and on
   the right is the stabilization by a single block.  This latter method
   produces the very large {twin bees shuttle spark} which is useful in
   a number of ways.  See {metamorphosis} for an example.  Adding a
   symmetrically placed block below this one suppresses the spark.  See
   also {p54 shuttle}.
	.**........................
	.**........................
	...........................
	...............*...........
	**.............**........**
	**..............**.......**
	...........**..**..........
	...........................
	...........................
	...........................
	...........**..**..........
	**..............**.........
	**.............**..........
	...............*...........
	...........................
	.**........................
	.**........................

:twin bees shuttle pair:  Any arrangement of two {twin bees shuttle}s
   such that they interact.  There are many ways that the two shuttles
   can be placed, either head-to-head, or else at right angles.  Glider
   guns can be constructed in at least five different ways.  Here is one
   by Bill Gosper in which the shuttles interact head-to-head:
	.................*...............................
	**...............**..............................
	**................**.............................
	.................**...........**.................
	.............................*.*.................
	.............................*...................
	.............................***.................
	.................**..............................
	..................**.............................
	.................**..............................
	.................*...........***.................
	.............................*.................**
	.............................*.*...............**
	..............................**.................
   For other examples, see {new gun}, {edge shooter}, {double-barrelled}
   and {natural Heisenburp}.

:twin bees shuttle spark:  The large and distinctive long-lived {spark}
   produced, most commonly, by the {twin bees shuttle}.  It starts off
   as shown below.
	..**.
	..**.
	.*..*
	*.**.
	*.**.
   After 3 generations it becomes {symmetric} along the horizontal axis,
   after 9 generations it becomes symmetric along the vertical axis
   also, and finally dies after 18 generations.
     Since the spark is isolated and long-lived, there are many possible
   {perturbation}s that it can perform.  One of the most useful is
   demonstrated in {metamorphosis} where a glider is converted into a
   {LWSS}.  Another useful one can turn a {LWSS} by 90 degrees:
	*..*.........
	....*........
	*...*.....*..
	.****....***.
	........*...*
	........**.**
	........**.**
	.............
	........**.**
	........**.**
	........*...*
	.........***.
	..........*..

:twinhat: (p1)  See also {hat} and {sesquihat}.
	..*...*..
	.*.*.*.*.
	.*.*.*.*.
	**.*.*.**
	....*....

:twin peaks:  = {twinhat}

:twirling T-tetsons II: (p60)  Found by Robert Wainwright.  This is a
   {pre-pulsar} {hassle}d by {killer toads}.
	.......**...**..........
	......*.......*.........
	.........*.*............
	.......**...**..........
	........................
	........................
	........................
	.....................***
	....................***.
	.............*..........
	***.........***.........
	.***....................
	....................***.
	.....................***
	........................
	.***....................
	***.........***.........
	.............*..........
	........................
	........................
	..........**...**.......
	............*.*.........
	.........*.......*......
	..........**...**.......

:TWIT:  = {eater5}

:two-arm:  The type of {universal constructor} exemplified by the
   original {Gemini} spaceship, where two independently programmed
   {construction arm}s sent gliders in pairs on 90-degree paths to
   collide with each other at the construction site.  Construction
   recipes for two-arm constructors are much more efficient in general,
   but they require many more {circuit}s and multiple independent data
   streams, which both tend to increase the complexity of
   {self-constructing} circuitry.  Compare {single-arm}.

:two-bit spark:  = {duoplet}.

:two eaters: (p3)  Found by Bill Gosper, September 1971.
	**.......
	.*.......
	.*.*.....
	..**.....
	.....**..
	.....*.*.
	.......*.
	.......**

:two pulsar quadrants: (p3)  Found by Dave Buckingham, July 1973.
   Compare {pulsar quadrant}.
	....*....
	....*....
	...**....
	..*......
	*..*..***
	*...*.*..
	*....*...
	.........
	..***....

:UC:  = {universal constructor}.

:underpopulation:  Death of a cell caused by it having fewer than two
   {neighbour}s.  See also {overpopulation}.

:unit cell:  = {unit Life cell}.

:unit Life cell:  A rectangular pattern, of size greater than 1x1, that
   can simulate Life in the following sense.  The pattern by itself
   represents a dead Life cell, and some other pattern represents a live
   Life cell.  When the plane is tiled by these two patterns (which then
   represent the state of a whole Life universe) they evolve, after a
   fixed amount of time, into another tiling of the plane by the same
   two patterns which correctly represents the Life generation following
   the one they initially represented.
     It is usual to use the prefix "meta-" for simulated Life features,
   so, for example, for the first known unit Life cell (constructed by
   David Bell in January 1996), one metatick is 5760 {tick}s, and one
   {metacell} is 500x500 cells.  Capital letters were originally used to
   make this distinction - e.g., Generation, Cell - but this usage is no
   longer common.
     In December 2005, Jason Summers constructed an analogous unit cell
   for Wolfram's Rule 110, a one-dimensional {cellular automaton} that
   is known be universal.  See also {OTCA metapixel}, {p1 megacell}.

:universal:  See {universal computer}, {universal constructor},
   {universal toolkit}.

:universal computer:  A computer that can compute anything that is
   computable.  (The concept of computability can be defined in terms of
   Turing machines, or by Church's lambda calculus, or by a number of
   other methods, all of which can be shown to lead to equivalent
   definitions.)  The relevance of this to Life is that both Bill Gosper
   and John Conway proved early on that it is possible to construct a
   universal computer in the Life universe.  (To prove the universality
   of a {cellular automaton} with simple rules was in fact Conway's aim
   in Life right from the start.)  Conway's proof is outlined in
   {Winning Ways}, and also in {The Recursive Universe}.
     Until recently, no universal Life computer had ever been built in
   practice  In April 2000, Paul Rendell completed a Turing machine
   construction (see {http://rendell-attic.org/gol/tm.htm} for details).
   This, however, has a finite tape, as opposed to the infinite tape of
   a true Turing machine, and is therefore not a universal computer.
   But in November 2002, Paul Chapman announced the construction of a
   universal computer, see
   {http://www.igblan.free-online.co.uk/igblan/ca/}. This is a universal
   register machine based around Dean Hickerson's
   {sliding block memory}.
     In 2009 Adam P. Goucher constructed a programmable {Spartan}
   universal computer/constructor pattern using stable {Herschel}
   circuitry.  It included memory tapes and registers capable of holding
   a simple universal instruction set and program data, and also a
   minimal {single-arm} universal constructor.  Its size meant that it
   was extremely impractical to program it to be {self-constructing},
   though this was theoretically possible if the escape of large numbers
   of gliders could be allowed as a side effect.
     In February 2010, Paul Rendell completed a universal Turing machine
   design with an unlimited tape, as described in his thesis at
   {http://eprints.uwe.ac.uk/22323/1/thesis.pdf}.
     In 2016 Nicolas Loizeau ("Coban") completed a Life pattern
   emulating a complete 8-bit programmable computer.
     See also {universal constructor}.

:universal constructor:  A pattern that is capable of constructing
   almost any pattern that has a {glider synthesis}.  This definition is
   a bit vague.  A precise definition seems impossible because it is not
   known, for example, whether all {still life}s are constructible.  In
   any case, a universal constructor ought to be able to construct
   itself in order to qualify as such.
     An outline of Conway's proof that such a pattern exists can be
   found in {Winning Ways}, and also in {The Recursive Universe}.  The
   key mechanism for the production of gliders with any given path and
   timing is known as side-tracking, and is based on the
   {kickback reaction}.  A universal constructor designed in this way
   can also function as a universal destructor:  it can delete almost
   any pattern that can be deleted by gliders.
     In May 2004, Paul Chapman and Dave Greene produced a prototype
   programmable universal constructor.  This is able to construct
   objects by means of {slow glider construction}s.  It likely that it
   could be programmed to construct itself, but the necessary program
   would be very large; moreover an additional mechanism would be needed
   in order to copy the program.
     A universal constructor is theoretically most useful when attached
   to a {universal computer}, which can be programmed to control the
   constructor to produce the desired pattern of gliders.  In what
   follows I will assume that a universal constructor always includes
   this computer.
     The existence of a universal constructor/destructor has a number of
   theoretical consequences.
     For example, the constructor could be programmed to make copies of
   itself.  This is a {replicator}.
     The constructor could even be programmed to make just one copy of
   itself translated by a certain amount and then delete itself. This
   would be a (very large, very high period) {spaceship}.  Any
   translation is possible, so that the spaceship could travel in any
   direction.  If the constructor makes a rotated but unreflected copy
   of itself, the result would be a looping spaceship or
   {reflectorless rotating oscillator}.
     The constructor could also travel slower than any given speed,
   since we could program it to perform some time-wasting task (such as
   repeatedly constructing and deleting a block) before copying itself.
   Of course, we could also choose for it to leave some debris behind,
   thus making a {puffer}.
     It is also possible to show that the existence of a universal
   constructor implies the existence of a {stable} {reflector}.  This
   proof is not so easy, however, and is no longer of much significance
   now that explicit examples of such reflectors are known.
     Progressively smaller universal-constructor mechanisms without an
   attached universal computer have been used in the
   {linear propagator}, {spiral growth} pattern, and the {Demonoid}s and
   {Orthogonoid}.  See also {single-channel}.
     Another strange consequence of the existence of universal
   constructors was pointed out by Adam P. Goucher and Tanner Jacobi in
   2015.  Any glider-constructible pattern, no matter how large, can be
   constructed with a fixed number of gliders, by working out a
   construction recipe for a universal constructor attached to a decoder
   that measures the distance to a faraway object.  The object's
   position encodes a numeric value that can be processed to retrieve as
   many bits of information as are needed to build a {slow salvo} to
   construct any given target pattern.  The simplest design, requiring
   less than a hundred gliders, is described in {reverse caber tosser}.

:universal destructor:  See {universal constructor}.

:universal register machine:  = {URM}

:universal regulator:  A {regulator} in which the incoming gliders are
   aligned to period 1, that is, they have arbitrary timing (subject to
   some minimum time required for the regulator to recover from the
   previous glider).
     Paul Chapman constructed the first universal regulator in March
   2003.  It is adjustable, so that the output can be aligned to any
   desired period.  A {stable} universal regulator was constructed by
   Dave Greene in September 2015, with a minimum delay between test
   signals of 1177 ticks.  Later stable versions have reduced the delay
   to 952 ticks.
     A universal regulator can allow two complex {circuit}s to interact
   safely, even if they have different base {period}s.  For example,
   signals from a {stable} logic circuit could be processed by a
   period-30 mechanism, though the precise timing of those signals would
   change in most cases.

:universal toolkit:  A set of Life reactions and mechanisms that can be
   used to construct any object that can be constructed by glider
   collisions.  Different universal toolkits were used to construct the
   {linear propagator}, {10hd Demonoid}, {0hd Demonoid}, and
   {Orthogonoid}, for example.

:universe:  The topology of the cells in the Life grid.  In the normal
   universe (the usual {Life} arena), the grid is infinite in both
   directions.  In a cylindrical universe, the grid is finite in one
   direction, and the cells at the two edges are adjacent to each other.
   In a {torus} universe, the grid is finite in both directions, and the
   cells at the top and bottom edges are adjacent, and the cells at the
   left and right edges are adjacent.  There are several other more
   obscure types of universe.
     Objects found in the cylindrical and toroidal universes can also
   run in the normal universe if an infinite number of copies are
   arranged to support each other.  Sometimes the objects can be
   supported in other ways to make a useful finite object.  This is one
   reason that {soup} searches are run in alternative universes, to find
   such objects.

:unix: (p6)  Two {block}s eating a {long barge}.  This is a useful
   {sparker}, found by Dave Buckingham in February 1976.  The name
   derives from the fact that it was for some time the mascot of the
   Unix lab of the mathematics faculty at the University of Waterloo.
	.**.....
	.**.....
	........
	.*......
	*.*.....
	*..*..**
	....*.**
	..**....

:unknown fate:  An object whose {fate} is in some way unanswerable with
   our current knowledge.  The simplest way that the fate of an object
   can be unknown involves the question of whether or not it exhibits
   infinite growth.  For example, the fate of the
   {Fermat prime calculator} is currently unknown, but its behaviour is
   otherwise predictable.
     A different type of unknown fate is that of the
   {Collatz 5N+1 simulator}, which may become stable, or an oscillator,
   or have an indefinitely growing bounding box.  Its behavior is
   otherwise predictable, and unlike the Fermat prime calculator the
   population is known to be bounded.
     Life objects having even worse behaviour (e.g. {chaotic growth})
   are not known as of July 2018.

:up boat with tail:  = {trans-boat with tail}

:U-pentomino:  Conway's name for the following {pentomino}, which
   rapidly dies.
	*.*
	***

:URM:  A universal register machine, particularly Paul Chapman's Life
   implementation of such a machine.  See {universal computer} for more
   information.

:vacuum:  Empty space.  That is, space containing only dead {cell}s.

:Venetian blinds:  The p2 {agar} obtained by using the pattern O..O to
   tile the plane. Period 2 stabilizations of finite patches of this
   agar are known.
	..................*.**.**......*......**.**.*..................
	..................**.*.*...**.*.*.**...*.*.**..................
	.....................*...*..*.*.*.*..*...*.....................
	.....................*..***...*.*...***..*.....................
	....................**.*.....*.*.*.....*.**....................
	.......................*..**.*...*.**..*.......................
	....................**..***..**.**..***..**....................
	................**.*.**...**.*****.**...**.*.**................
	................**.**....*...........*....**.**................
	...................*..**.*.*.......*.*.**..*...................
	................**..***..**.*******.**..***..**................
	........**..**.*.**...**.*************.**...**.*.**..**........
	.....*..*...**.**....*...................*....**.**...*..*.....
	....*.*.*......*..**.*.*...............*.*.**..*......*.*.*....
	...*..*.**..**..***..**.***************.**..***..**..**.*..*...
	...*.**....*.**...**.*********************.**...**.*....**.*...
	**.**...**.**....*...........................*....**.**...**.**
	*.*...**.*.*..**.*.*.......................*.*.**..*.*.**...*.*
	..*.**.*.*..***..**.***********************.**..***..*.*.**.*..
	..*.*..****...**.*****************************.**...****..*.*..
	.**..*.......*...................................*.......*..**.
	*..*.*....**.*.*...............................*.*.**....*.*..*
	.*.*..*****..**.*******************************.**..*****..*.*.
	..*.***..***.*************************************.***..***.*..
	....*.*..*...........................................*..*.*....
	..*.*.*..*.*.......................................*.*..*.*.*..
	..**...*.**.***************************************.**.*...**..
	.........*********************************************.........
	...............................................................
	...............................................................
	.........*********************************************.........
	..**...*.**.***************************************.**.*...**..
	..*.*.*..*.*.......................................*.*..*.*.*..
	....*.*..*...........................................*..*.*....
	..*.***..***.*************************************.***..***.*..
	.*.*..*****..**.*******************************.**..*****..*.*.
	*..*.*....**.*.*...............................*.*.**....*.*..*
	.**..*.......*...................................*.......*..**.
	..*.*..****...**.*****************************.**...****..*.*..
	..*.**.*.*..***..**.***********************.**..***..*.*.**.*..
	*.*...**.*.*..**.*.*.......................*.*.**..*.*.**...*.*
	**.**...**.**....*...........................*....**.**...**.**
	...*.**....*.**...**.*********************.**...**.*....**.*...
	...*..*.**..**..***..**.***************.**..***..**..**.*..*...
	....*.*.*......*..**.*.*...............*.*.**..*......*.*.*....
	.....*..*...**.**....*...................*....**.**...*..*.....
	........**..**.*.**...**.*************.**...**.*.**..**........
	................**..***..**.*******.**..***..**................
	...................*..**.*.*.......*.*.**..*...................
	................**.**....*...........*....**.**................
	................**.*.**...**.*****.**...**.*.**................
	....................**..***..**.**..***..**....................
	.......................*..**.*...*.**..*.......................
	....................**.*.....*.*.*.....*.**....................
	.....................*..***...*.*...***..*.....................
	.....................*...*..*.*.*.*..*...*.....................
	..................**.*.*...**.*.*.**...*.*.**..................
	..................*.**.**......*......**.**.*..................

:very long:  = {long long}

:very long house:  The following {induction coil}.
	.*****.
	*..*..*
	**...**

:volatility:  The volatility of an {oscillator} is the size (in cells)
   of its {rotor} divided by the sum of the sizes of its rotor and its
   {stator}.  In other words, it is the proportion of cells involved in
   the oscillator which actually oscillate.  For many periods there are
   known oscillators with volatility 1, see for example {Achim's p16},
   {figure-8}, {Kok's galaxy}, {mazing}, {pentadecathlon}, {phoenix},
   {relay}, {smiley} and {tumbler}.  Such an oscillator of period 3 was
   found in August 2012 by Jason Summers.
	.........*.*.....*...*.....*.*.
	........*...*....*...*....*...*
	.........*.......*...*.......*.
	...........**.**.*...*.**.**...
	.................*...*.........
	..........*...*.........*...*..
	........*.*.................*.*
	...............................
	........*...................*..
	.......**..................**..
	.......*...................*...
	.....*..*................*..*..
	*....*..............*....*.....
	****.**.***.........****.**.***
	***.**.****.........***.**.****
	.....*....*..............*....*
	..*..*................*..*.....
	...*...................*.......
	..**..................**.......
	..*...................*........
	...............................
	*.*.................*.*........
	..*...*.........*...*..........
	.........*...*.................
	...**.**.*...*.**.**...........
	.*.......*...*.......*.........
	*...*....*...*....*...*........
	.*.*.....*...*.....*.*.........
     The smallest period for which the existence of such statorless
   oscillators is undecided is 7. There are oscillators with volatility
   arbitrarily close to 1 for all but finitely many periods, because of
   the possibility of feeding the gliders from a {true} period n {gun}
   into an {eater}.
     The term "volatility" is due to Robert Wainwright.  See also
   {strict volatility}.

:volcano:  Any of a number of p5 oscillators which produce sparks.  See
   {lightweight volcano}, {middleweight volcano} and
   {heavyweight volcano}.

:von Neumann neighbourhood:  The set of all cells that are orthogonally
   adjacent to a cell or group of cells.  The von Neumann neighbourhood
   of a cell can be thought of as the points at a Manhattan distance of
   1 from that cell.  Compare {Moore neighbourhood}.
     Cell neighbourhoods can also be defined with a higher range. The
   von Neumann neighbourhood of range n can be defined recursively as
   the von Neumann neighbourhood of the von Neumann neighbourhood of
   range n-1.  For example, the von Neumann neighbourhood of range 2 is
   the set of all cells that are orthogonally adjacent to the range-1
   von Neumann neighbourhood.

:V-pentomino:  Conway's name for the following {pentomino}, a {loaf}
   {predecessor}.
	*..
	*..
	***

:V spark:  A common three-bit {polyplet} {spark}, produced most notably
   by the {pentadecathlon}.
	*.*
	.*.
   The spark can convert a {pre-block} or {block} into a {glider} as
   shown here:
	.*...
	**..*
	...*.
	....*
   Also see {PD-pair reflector}.

:Wainwright's tagalong:  A small p4 c/4 diagonal {tagalong} that has 7
   cells in every phase.  It is shown here attached to the back of a
   {Canada goose}.
	***.............
	*.........**....
	.*......***.*...
	...**..**.......
	....*...........
	........*.....*.
	....**...*...**.
	...*.*.**....*.*
	...*.*..*.**.*..
	..*....**.....*.
	..**............
	..**............

:washerwoman: (2c/3 p18 fuse)  A {fuse} discovered by Earl Abbe,
   published in {LifeLine} Vol 3, September 1971.
	*.......................................................
	**....*.....*.....*.....*.....*.....*.....*.....*.....*.
	***..*.*...*.*...*.*...*.*...*.*...*.*...*.*...*.*...*.*
	**....*.....*.....*.....*.....*.....*.....*.....*.....*.
	*.......................................................

:washing machine: (p2)  Found by Robert Wainwright before June 1972.
	.**.**.
	*.**..*
	**....*
	.*...*.
	*....**
	*..**.*
	.**.**.

:wasp: (c/3 orthogonally, p3)  The following {spaceship} which produces
   a {domino} {spark} at the back.  It is useful for {perturb}ing other
   objects.  Found by David Bell, March 1998.
	..........**.**.......
	........**.*.**.**....
	.....***.*..***..****.
	.***....***.....*....*
	*.*.*.***.*........**.
	*.*.*.****............
	.*.*....*..*..........
	..........*...........
	..*...................
	..*...................

:waterbear: ((23,5)c/79 obliquely, p158) A {self-supporting} oblique
   {macro-spaceship} constructed by Brett Berger on December 28, 2014.
   It is currently the fastest oblique macro-spaceship in Conway's Game
   of Life by several orders of magnitude, and is also the smallest
   known oblique macro-spaceship in terms of bounding box, superseding
   the {Parallel HBK}.  It is no longer the smallest or fastest oblique
   spaceship due to the discovery in 2018 of the {elementary}
   {knightship} {Sir Robin}.
     Previous oblique spaceships, the {Gemini} and the
   {half-baked knightship}s, are stationary throughout almost all of
   their life cycles, as they construct the necessary mechanisms to
   support a sudden short move.  The waterbear constructs support for
   {reburnable fuse} reactions involving {(23,5)c/79 Herschel climber}s
   that are in constant motion.

:wave:  A wick-like structure attached at both ends to moving
   spaceship-like patterns, in such a way that the entire pattern is
   mobile.  Especially if the wave gets longer over time, the supporting
   patterns are {wavestretcher}s.
     Also, the gliders or spaceships emitted by a rake may be referred
   to as a wave, again because the line as a whole appears to move in a
   different direction from the individual components, due to the rake's
   movement.  Compare with {stream}.
     In general a wave can be interpreted as moving at a variety of
   different velocities, depending on which specific subcomponents are
   chosen as the starting and ending points for calculating speed and
   direction.  See {antstretcher}, {wavestretcher} for a practical
   example of identical wave ends being connected to spaceships with
   different velocities.

:wavefront: (p4)  Found by Dave Buckingham, 1976 or earlier.
	........**...
	........*....
	.........*...
	........**...
	.....**...**.
	....*..***..*
	....*.....**.
	.....*...*...
	**.*.*...*...
	*.**.*.**....
	....*.*......
	....*.*......
	.....*.......

:waveguide:  = {superstring}.

:wavestretcher:  A {spaceship} pattern that supports a connection to an
   extensible periodic {wick}-like structure, whose speed and/or
   direction of propagation are different from those of the
   wavestretcher spaceship.
     Connecting the following to a standard diagonal {antstretcher}
   creates a new oblique {wavestretcher} (a type of {growing spaceship})
   and also an alternate {space nonfiller} mechanism.
	.......................................................*.....
	.......................................................**....
	.....................................................*..*....
	....................................................*........
	.................................................**..*.......
	................................................*..*.........
	.................................................*...........
	.............................................*...**..........
	............................................*.**.............
	...........................................**..*.............
	...........................................**.**.............
	...........................................*..*..**..........
	..........................................**......**.........
	...........................................*.**.*.**.........
	..........................................*.***.*............
	..........................................*.*.*.*............
	.............................................................
	........................................*...*................
	.......................................**....................
	.....................................***..*..................
	..................................**.**......................
	...................................*.........................
	....................................*.*......................
	...................................*.........................
	...................................*..*......................
	..................................*..........................
	.....................................*.......................
	..................................****.......................
	................................*.**.*.......................
	.....................................*.......................
	................................*............................
	.................................*..*........................
	...................................*.........................
	.........................*....***....................***.....
	**......................*.***....*......................*...*
	..**.**.................*..*....*....................*...*...
	..**...**.**...............*..*................**.*...*.****.
	**.....**...**.**.........**.***...**..**.***.*....*.....*..*
	.....**.....**...**.**......*.**..*.*..***.**.*.*...*......*.
	..........**.....**...**.*...*....*.*.*..**..*..*...****.....
	...............**.....**..*.*.**..*..*.......................
	....................**...........*....*..........**...**.....
	.......................................*..........*..........
	....................................*........................
	....................................**.......................
   A required supporting c/5 {spark} is shown at the right edge.  It can
   be supplied by a {spider} or another c/5 orthogonal spaceship with a
   similar {edge spark}.  Alternatively, the c/5 component could
   theoretically be replaced by a supporting spaceship travelling
   diagonally at c/6, to support the same oblique trail of ants.  As of
   June 2018 no workable c/6 component has been found.

:wedge:  A 26-cell quadratic growth pattern found by Nick Gotts in March
   2006, based on ideas found in {metacatacryst} and {Gotts dots}.  It
   held the record for the smallest-population quadratic growth pattern
   for eight years, until it was surpassed by
   {25-cell quadratic growth}.  See {switch-engine ping-pong} for the
   lowest-population {superlinear growth} pattern as of July 2018, along
   with a list of the record-holders.

:wedge grow:  = {wedge}.

:weekender: (2c/7 orthogonally, p7)  Found by David Eppstein in January
   2000.  In April 2000 Stephen Silver found a tagalong for a pair of
   weekenders.  At present, n weekenders pulling n-1 tagalongs
   constitute the only known {spaceship}s of this speed or period,
   except for variants of the {weekender distaff} that suppress its
   output gliders.
	.*............*.
	.*............*.
	*.*..........*.*
	.*............*.
	.*............*.
	..*...****...*..
	......****......
	..****....****..
	................
	....*......*....
	.....**..**.....

:weekender distaff: (2c/7, p16982)  The first orthogonal 2c/7 rake,
   constructed by Ivan Fomichev on May 22nd, 2014.  It uses the weak
   {spark}s from {weekender}s to perturb an LWSS into an active reaction
   in a variable-period loop, which produces a series of {slow salvo}
   gliders that finally rebuilds the LWSS.

:weld:  To join two or more {still life}s or {oscillator}s together.
   This is often done in order to fit the objects into a smaller space
   than would otherwise be possible.  The simplest useful example is
   probably the {integral sign}, which can be considered as a pair of
   welded {eater1}s.

:Wheels, Life, and other Mathematical Amusements:  One of Martin
   Gardner's books (1983) that collects together material from his
   column in Scientific American.  The last three chapters of this book
   contain all the Life stuff.

:why not: (p2)  Found by Dave Buckingham, July 1977.
	...*...
	...*.*.
	.*.....
	*.*****
	.*.....
	...*.*.
	...*...

:wick:  A stable or oscillating linearly repeating pattern that can be
   made to {burn} at one end.  See {fuse}.  Wicks are often fairly
   dense, with repeating units directly connected or at least adjacent
   to each other, as in the beehive {lightspeed wire} for example.
   However, sparse wicks such as the blocks in the
   {31c/240 Herschel-pair climber} are known, and arbitrarily sparse
   wicks can be constructed.

:wickstretcher:  A {spaceship}-like object which stretches a {wick} that
   is fixed at the other end.  The wick here is assumed to be in some
   sense connected, otherwise most {puffer}s would qualify as
   wickstretchers.  The first example of a wickstretcher was found in
   October 1992 (front end by Hartmut Holzwart and back end by Dean
   Hickerson) and stretches {ants} at a speed of c/4.  This is shown
   below with an improved back end found by Hickerson the following
   month.
	.................**..............................
	.............**....*.............................
	............***.*................................
	*.**..**...*...****.*.*....**.......**...........
	*....**..*........*.***....*....**.*..*.**.*.....
	*.**....**.**....*...........*...*.*.**.*.**.....
	......*.......*.............**.....*..*.*...**...
	.....*.........*.*....***...*....*..*.*.***...*..
	.....*.........*.*....***.**.*..**.*.*...*..**.*.
	......*.......*.............**.*...**....**....*.
	*.**....**.**....*..........*........**.*.*.**.**
	*....**..*........*.***........*...*...**.*..*.*.
	*.**..**...*...****.*.*.......*.*...**....*..*.*.
	............***.*..............*.....*.***....*..
	.............**....*.................*.*.........
	.................**...................*..........
     Diagonally moving c/4 and c/12 wickstretchers have also been built:
   see {tubstretcher} and {linestretcher}.  In July 2000 Jason Summers
   constructed a c/2 wickstretcher, stretching a p50 {traffic jam} wick,
   based on an earlier (October 1994) pattern by Hickerson.  A c/5
   diagonal wickstretcher was found in January 2011 by Matthias
   Merzenich, who also discovered a c/5 orthogonal wickstretcher two
   years later in March 2013.

:wicktrailer:  Any {extensible} {tagalong} or {component} that can be
   attached to itself, as well as to the back of a {spaceship}.  The
   number of generations that it takes for the component to occur again
   in the same place is often called the period of the wicktrailer.
   This has little relation to the period of the component.  See
   {branching spaceship} for an example of a wicktrailer that is part of
   a p2 spaceship, but repeats itself in the same location at period 20.

:windmill: (p4)  Found by Dean Hickerson, November 1989.
	...........*......
	.........**.*.....
	.......**.........
	..........**......
	.......***........
	..................
	***...............
	...**..***.**.....
	..........*******.
	.*******..........
	.....**.***..**...
	...............***
	..................
	........***.......
	......**..........
	.........**.......
	.....*.**.........
	......*...........

:wing:  The following {induction coil}.  This is generation 2 of
   {block and glider}.
	.**.
	*..*
	.*.*
	..**
     In an unrelated use, "wing" may also refer to an {arm} of a
   spaceship.

:WinLifeSearch:  Jason Summers' GUI version of {lifesrc} for MS Windows.
   It is available from {http://entropymine.com/jason/life/software/}.

:Winning Ways:  A two-volume book (1982) by Elwyn Berlekamp, John Conway
   and Richard Guy on mathematical games.  The last chapter of the
   second volume concerns Life, and outlines a proof of the existence of
   a {universal constructor}.

:wire:  A repeating stable structure, usually fairly dense, that a
   {signal} can travel along without making any permanent change.  Known
   wires include the diagonal {2c/3 wire}, and orthogonal
   {lightspeed wire} made from a chain of beehives.  Diagonal lightspeed
   wires are known, but the required signals are fairly complex and have
   no known {glider synthesis}.

:with the grain:  A term used for {negative spaceship}s travelling in
   {zebra stripes} agar, parallel to the stripes, and also for
   {with-the-grain grey ship}s.
     Below are three small examples of "negative spaceships" found by
   Gabriel Nivasch in July 1999, travelling with the grain through a
   stabilized finite segment of zebra stripes agar:
	.*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*.
	.****************************************************.
	......................................................
	.****************************************************.
	*....................................................*
	.****************************************************.
	................................................*.....
	.****************************************.****....***.
	*.........................................**.....*...*
	.**************************************.....*********.
	.............................................*........
	.************************************.........**..***.
	*.....................................*.*.....**.*...*
	.************************************...*.....***.***.
	.............................................*........
	.**************************************.....*********.
	*.........................................**.....*...*
	.****************************************.****....***.
	................................................*.....
	.****************************************************.
	*....................................................*
	.****************************************************.
	......................................................
	.*************************..***..***..***..**********.
	*..........................**...**...**...**..*......*
	.***********************...*....*....*....*.....*****.
	...........................**...**...**...**...*......
	.*************************..***..***..***..**********.
	*....................................................*
	.****************************************************.
	......................................................
	.****************************************************.
	*....................................................*
	.****************************************************.
	......................................................
	.***********************..***..***..***..***..*******.
	*........................**...**...**...**...**......*
	.***********************...**...**...**...**...******.
	................................................*.....
	.*********************...........................****.
	*................................................*...*
	.*********************...........................****.
	................................................*.....
	.***********************...**...**...**...**...******.
	*........................**...**...**...**...**......*
	.***********************..***..***..***..***..*******.
	......................................................
	.****************************************************.
	*....................................................*
	.****************************************************.
	......................................................
	.****************************************************.
	.*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*..*.
   It has been proven that signals travelling non-destructively with the
   grain through zebra stripes cannot travel at less than the
   {speed of light}.

:with-the-grain grey ship:  A {grey ship} in which the region of density
   1/2 consists of lines of ON cells lying parallel to the direction in
   which the spaceship moves.  See also {against-the-grain grey ship}.

:WLS:  =  {WinLifeSearch}

:worker bee: (p9)  Found by Dave Buckingham in 1972.  Unlike the similar
   {snacker} this produces no {spark}s, and so is not very important.
   Like the snacker, the worker bee is {extensible}.  It is, in fact, a
   finite version of the infinite oscillator which consists of six ON
   cells and two OFF cells alternating along a line.  Note that Dean
   Hickerson's new snacker ends also work here.
	**............**
	.*............*.
	.*.*........*.*.
	..**........**..
	................
	.....******.....
	................
	..**........**..
	.*.*........*.*.
	.*............*.
	**............**

:W-pentomino:  Conway's name for the following {pentomino}, a common
   {loaf} {predecessor}.
	*..
	**.
	.**

:*WSS:  Any of the standard orthogonal {spaceship}s - {LWSS}, {MWSS}, or
   {HWSS}.  At one point the term {fish} was more common for this group
   of spaceships.

:x66: (c/2 orthogonally, p4)  Found by Hartmut Holzwart, July 1992. Half
   of this can be escorted by an HWSS.  The name refers to the fact that
   every cell (live or dead) has at most 6 live neighbours (in contrast
   to {spaceship}s based on {LWSS}, {MWSS} or {HWSS}). In fact this
   spaceship was found by a search with this restriction.
	..*......
	**.......
	*..***..*
	*....***.
	.***..**.
	.........
	.***..**.
	*....***.
	*..***..*
	**.......
	..*......

:Xlife:  A popular freeware Life program that runs under the X Window
   System.  The main Life code was written by Jon Bennett, and the X
   code by Chuck Silvers.

:X-pentomino:  Conway's name for the following {pentomino}, a
   {traffic light} {predecessor}.
	.*.
	***
	.*.

:Y-pentomino:  Conway's name for the following {pentomino}, which
   rapidly dies.
	..*.
	****

:zebra stripes: (p1)  A stable agar consisting of alternating bands of
   live and dead cells. Known {spacefiller}s and many {gray ship}s
   create patches of this agar. It is also the medium through which
   {with the grain} and {against the grain} {negative spaceship}s
   travel.  Many simple stabilizations of the boundaries of finite
   regions of this agar are known, as shown below.
	..**.......................
	..*........................
	....*..*..*..*..*..*..*....
	...********************....
	..*........................
	...******************......
	.....................*.....
	.********************......
	*..........................
	.**********************....
	.......................*.**
	.********************..*.**
	*....................*.*...
	.********************..*...
	.......................**..
	...******************......
	..*..................*.....
	...******************......
	...........................
	.....**..**.*.****.**......
	.....**..*.**.*..*.**......

:Z-hexomino:  The following {hexomino}.  The Z-hexomino features in the
   {pentoad}, and also in {Achim's p144}.
	**.
	.*.
	.*.
	.**

:zone of influence:  The set of cells on which a chosen cell or pattern
   can potentially exert an influence in a given number of generations
   N. If N is not specified it is generally taken to be one, in which
   case the zone of influence simply coincides with the Moore
   neighbourhood of the cell or pattern.
     The set for N generations consists of all the cells to which at
   least N paths of length N can be traced from the cell(s) in question.
   Contrast this with the range-N Moore neighbourhood, which consists of
   all cells to which at least one path of length n can be traced.

:Z-pentomino:  Conway's name for the following {pentomino}, which
   rapidly dies.
	**.
	.*.
	.**

:zweiback: (p30)  An oscillator in which two {HW volcano}es {hassle} a
   {loaf}.  This was found by Mark Niemiec in February 1995.  A smaller
   version using Scot Ellison's reduced HW volcano is shown below.
	..........*..............................
	........*****.................*..........
	.......*.....*..............*****........
	.......*..**.*.............*.....*.......
	...*.***.*.*.**............*.**..*.......
	...**....*................**.*.*.***.*...
	......**.**....................*....**...
	.*****.*.*..*.................**.**......
	*......*...*.*..............*..*.*.*****.
	**..*****.**.*.............*.*...*......*
	............**.............*.**.*****..**
	.....**....***.............**............
	.....**....***.....**......***....**.....
	............**....*..*.....***....**.....
	**..*****.**.*.....*.*.....**............
	*......*...*.*......*......*.**.*****..**
	.*****.*.*..*..............*.*...*......*
	......**.**.................*..*.*.*****.
	...**....*....................**.**......
	...*.***.*.*.**................*....**...
	.......*..**.*............**.*.*.***.*...
	.......*.....*.............*.**..*.......
	........*****..............*.....*.......
	..........*.................*****........
	..............................*..........

-----------------------------------------------------------------------

Bibliography.

David I. Bell, "Spaceships in Conway's Life".  Series of articles
  posted on comp.theory.cell-automata, Aug-Oct 1992.  Now available
  from his website (http://tip.net.au/~dbell/).

David I. Bell, "Speed c/3 Technology in Conway's Life", 17 December
  1999.  Available from his website (see above).

Elwyn R. Berlekamp, John H. Conway and Richard K. Guy, "Winning Ways
  for your Mathematical Plays, II: Games in Particular".  Academic
  Press, 1982.

David J Buckingham, "Some Facts of Life".  BYTE, December 1978.

Dave Buckingham, "My Experience with B-heptominos in Oscillators".
  12 October 1996.  Available from Paul Callahan's website
  (http://conwaylife.com/ref/lifepage/patterns/bhept/bhept.html).

David J. Buckingham and Paul B. Callahan, "Tight Bounds on Periodic Cell
  Configurations in Life".  Experimental Mathematics 7:3 (1998) 221-241.
  Available at http://tinyurl.com/TightBoundsOnCellConfigs .

Noam D. Elkies, "The still-Life density problem and its
  generalizations", pp228-253 of "Voronoi's Impact on Modern Science,
  Book I", P. Engel, H. Syta (eds), Institute of Mathematics,
  Kyiv 1998 = Vol.21 of Proc. Inst. Math. Nat. Acad. Sci. Ukraine,
  math.CO/9905194 (http://front.math.ucdavis.edu/math.CO/9905194).

Martin Gardner, "Wheels, Life, and other Mathematical Amusements".
  W. H. Freeman and Company, 1983.

R. Wm. Gosper, "Exploiting Regularities in Large Cellular Spaces".
  Physica 10D (1984) 75-80.

N. M. Gotts and P. B. Callahan, "Emergent structures in sparse fields of
  Conway's 'Game of Life'", in "Artificial Life VI: Proceedings of the
  Sixth International Conference on Artificial Life", MIT Press, 1998.

Mark D Niemiec, "Life Algorithms".  BYTE, January 1979.

William Poundstone, "The Recursive Universe".  William Morrow and
  Company Inc., 1985.
