proposition: Lemma bigcup_set0_subset {A B} (s : set B) (f : A -> set B) : \bigcup_(x in set0) (f x) \subset s.
proof: Proof. firstorder. Qed.
imports: mathcomp.ssreflect.ssreflect Classes.RelationClasses Classes.Morphisms List Tactics mathcomp(ssrfun ssrbool ssrnat seq)