(VAR x y )
(RULES 
        +(x, 0) -> x
        +(x, s(y)) -> s(+(x, y))
        *(x, 0) -> 0
        *(x, s(y)) -> +(*(x, y), x)
        ge(x, 0) -> true
        ge(0, s(y)) -> false
        ge(s(x), s(y)) -> ge(x, y)
        -(x, 0) -> x
        -(s(x), s(y)) -> -(x, y)
        fact(x) -> iffact(x, ge(x, s(s(0))))
        iffact(x, true) -> *(x, fact(-(x, s(0))))
        iffact(x, false) -> s(0)
        
)