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