(VAR x y )
(RULES 
        p(0) -> 0
        p(s(x)) -> x
        le(0, y) -> true
        le(s(x), 0) -> false
        le(s(x), s(y)) -> le(x, y)
        minus(x, 0) -> x
        minus(x, s(y)) -> if(le(x, s(y)), 0, p(minus(x, p(s(y)))))
        if(true, x, y) -> x
        if(false, x, y) -> y
        
)