proposition: Lemma binunion_assoc x y z : (x ∪ y) ∪ z = x ∪ (y ∪ z).
proof: Proof. Proof using VIEQ M_ZF. 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 ZF) Undecidability.FOL.Sets(ZF binZF) Undecidability.FOL.Sets.Models(Aczel Aczel_CE Aczel_TD) Coq(Lia)