#[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.