proposition: Lemma binunion_assoc x y z : (x ∪ y) ∪ z = x ∪ (y ∪ z).
proof: Proof. Proof using M_ZF VIEQ. apply M_ext; intros a [H|H] % binunion_el; eauto. - apply binunion_el in H as [H|H]; eauto. - apply binunion_el in H as [H|H]; eauto. 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