TRS:
 {      leq(0(), y) -> true(),
     leq(s(x), 0()) -> false(),
    leq(s(x), s(y)) -> leq(x, y),
   if(true(), x, y) -> x,
  if(false(), x, y) -> y,
          -(x, 0()) -> x,
      -(s(x), s(y)) -> -(x, y),
        mod(0(), y) -> 0(),
     mod(s(x), 0()) -> 0(),
    mod(s(x), s(y)) -> if(leq(y, x), mod(-(s(x), s(y)), s(y)), s(x))}
 Fail