proposition: Lemma binunion_el x y z : x ∈ y ∪ z <-> x ∈ y \/ x ∈ z.
proof: Proof. Proof using M_ZF VIEQ. split. - intros [u [H1 H2]] % M_union. apply M_pair in H1 as [->| ->]; auto. - intros [H|H]. + apply M_union. exists y. rewrite M_pair. auto. + apply M_union. exists z. rewrite M_pair. auto. Qed.
imports: Undecidability.FOL(Syntax.Facts Semantics.Tarski.FullFacts) Undecidability.FOL(Sets.ZF) Undecidability.FOL(ZF) Undecidability.FOL.TRAKHTENBROT(hfs) Undecidability.Shared.Libs.DLW.Utils(finite) Undecidability(Shared.ListAutomation) Lia