proposition: Lemma pair_com x y : {x; y} = {y; x}.
proof: Proof. Proof using VIEQ M_ZF. apply M_ext; intros z [->| ->] % M_pair; apply M_pair; auto. 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)