Program Definition contains (l h: Z) (s: t) :=
  if zlt l h then R.contains l h s else true.

(* Specifications: *)
Theorem contains_spec: forall l h s, contains l h s = true <-> (forall x, l <= x < h -> In x s).
Theorem contains_spec: forall l h s, contains l h s = true <-> (forall x, l <= x < h -> In x s).