(VAR x y z)
(THEORY (AC plus times))
(RULES
  plus(x, 0) -> x
  plus(s(x), y) -> s(plus(x, y))
  times(x, 0) -> 0
  times(s(x), y) -> plus(times(x, y), y)
  times(x, plus(y, z)) -> plus(times(x, y), times(x, z))
)