TRS:
 {           le(0(), y) -> true(),
          le(s(x), 0()) -> false(),
         le(s(x), s(y)) -> le(x, y),
          minus(x, 0()) -> x,
          minus(0(), x) -> 0(),
      minus(s(x), s(y)) -> minus(x, y),
            gcd(0(), y) -> y,
         gcd(s(x), 0()) -> s(x),
        gcd(s(x), s(y)) -> if_gcd(le(y, x), s(x), s(y)),
   if_gcd(true(), x, y) -> gcd(minus(x, y), y),
  if_gcd(false(), x, y) -> gcd(minus(y, x), x)}
 Fail