MAYBE
Trs:
 {       le(0(), y) -> true(),
      le(s(x), 0()) -> false(),
     le(s(x), s(y)) -> le(x, y),
   if(true(), x, y) -> 0(),
  if(false(), x, y) -> s(minus(p(x), y)),
             p(0()) -> 0(),
            p(s(x)) -> x,
        minus(x, y) -> if(le(x, y), x, y)}
 Comment:
  We consider a duplicating trs.
  FAIL:
   Open