(VAR x y )
(RULES 
        f(0) -> s(0)
        f(s(0)) -> s(s(0))
        f(s(0)) -> *(s(s(0)), f(0))
        f(+(x, s(0))) -> +(s(s(0)), f(x))
        f(+(x, y)) -> *(f(x), f(y))
        
)