proposition: Lemma set_eq_isSome_complete {A} (s : set (option A)) (s' : set A) : isSome :&: s <--> Some @: s' -> Some @: s' \subset s.
proof: Proof. intros H. rewrite <- H. firstorder. Qed.
imports: mathcomp.ssreflect.ssreflect Classes.RelationClasses Classes.Morphisms List Tactics mathcomp(ssrfun ssrbool ssrnat seq)