TRS:
 {         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))}
 Fail