---
sum := sum subtract sum
  sum := sum plus sum
    sum := "INT"
      INT "1" (1, 1)
    plus := "+"
      + "+" (1, 3)
    sum := sum divide sum
      sum := sum multiply sum
        sum := "INT"
          INT "2" (1, 5)
        multiply := "*"
          * "*" (1, 7)
        sum := "INT"
          INT "3" (1, 9)
      divide := "/"
        / "/" (1, 11)
      sum := "INT"
        INT "4" (1, 13)
  subtract := "-"
    - "-" (1, 15)
  sum := "INT"
    INT "5" (1, 17)