proposition: Lemma union_as_family_union (U V : Ensemble T) : Union U V = FamilyUnion (Couple U V).
proof: Proof. extensionality_ensembles_inv; subst. - exists U; firstorder. - exists V; firstorder. - left. assumption. - right. assumption. Qed.
imports: Coq(Classical_Prop) Coq(Classical_sets) Coq(Morphisms) ZornsLemma(Image ImageImplicit) ZornsLemma(EnsemblesImplicit)