Global Hint Rewrite remove_spec : rb.
#[global]
Instance remove_ok s x `{Ok s} : Ok (remove x s).
(** ** Removing the minimal element *)

Lemma delmin_spec l y r c x s' `{O : Ok (Node c l y r)} :
delmin l y r = (x,s') ->
min_elt (Node c l y r) = Some x /\ del x (Node c l y r) = s'.