(VAR x y z )
(RULES 
        minus(minus(x, y), z) -> minus(x, plus(y, z))
        minus(0, y) -> 0
        minus(x, 0) -> x
        minus(s(x), s(y)) -> minus(x, y)
        plus(0, y) -> y
        plus(s(x), y) -> plus(x, s(y))
        plus(s(x), y) -> s(plus(y, x))
        zero(s(x)) -> false
        zero(0) -> true
        p(s(x)) -> x
        p(0) -> 0
        div(x, y) -> quot(x, y, 0)
        quot(s(x), s(y), z) -> quot(minus(p(ack(0, x)), y), s(y), s(z))
        quot(0, s(y), z) -> z
        ack(0, x) -> s(x)
        ack(0, x) -> plus(x, s(0))
        ack(s(x), 0) -> ack(x, s(0))
        ack(s(x), s(y)) -> ack(x, ack(s(x), y))
        
)