MAYBE
Trs:
 {    min(0(), y) -> 0(),
  min(s(x), s(y)) -> s(min(x, y)),
      min(x, 0()) -> 0(),
      max(0(), y) -> y,
  max(s(x), s(y)) -> s(max(x, y)),
      max(x, 0()) -> x,
    -(s(x), s(y)) -> -(x, y),
        -(x, 0()) -> x,
   gcd(0(), s(y)) -> s(y),
   gcd(s(x), 0()) -> s(x),
  gcd(s(x), s(y)) -> gcd(-(s(max(x, y)), s(min(x, y))), s(min(x, y)))}
 Comment:
  We consider a duplicating trs.
  FAIL:
   Open