#[global]
Instance remove_min_ok l x r : forall h `(Ok (Node h l x r)),
 Ok (remove_min l x r)#1.

(* Specifications: *)
Lemma remove_min_gt_tree : forall l x r h `{Ok (Node h l x r)}, gt_tree (remove_min l x r)#2 (remove_min l x r)#1.
Lemma merge_spec : forall s1 s2 y, InT y (merge s1 s2) <-> InT y s1 \/ InT y s2.