Global Instance empty_ok : Ok empty.

(* Specifications: *)
Lemma empty_spec : Empty empty.
Lemma is_empty_spec : forall s : t, is_empty s = true <-> Empty s.
Lemma elements_spec1 : forall (s : t) (x : elt), In x (elements s) <-> In x s.
Lemma elements_spec2 : forall (s : t) (Hs : Ok s), sort X.lt (elements s).
Lemma elements_spec2w : forall (s : t) (Hs : Ok s), NoDupA X.eq (elements s).
Lemma min_elt_spec1 : forall (s : t) (x : elt), min_elt s = Some x -> In x s.
Lemma min_elt_spec2 : forall (s : t) (x y : elt) (Hs : Ok s), min_elt s = Some x -> In y s -> ~ X.lt y x.
Lemma min_elt_spec3 : forall s : t, min_elt s = None -> Empty s.
Lemma max_elt_spec1 : forall (s : t) (x : elt), max_elt s = Some x -> In x s.
Lemma max_elt_spec2 : forall (s : t) (x y : elt) (Hs : Ok s), max_elt s = Some x -> In y s -> ~ X.lt x y.
Lemma max_elt_spec3 : forall s : t, max_elt s = None -> Empty s.