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