proposition: Lemma M_ext x y : x ⊆ y -> y ⊆ x -> x = y.
proof: Proof. Proof using VIEQ M_ZF. rewrite <- VIEQ. apply (@M_ZF (fun _ => ∅) ax_ext). cbn; tauto. 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)