proposition: Lemma opair_inj1 x x' y y' : M_opair x y = M_opair x' y' -> x = x'.
proof: Proof. Proof using VIEQ M_ZF. intros He. assert (H : {x; x} ∈ M_opair x y) by apply M_pair1. rewrite He in H. apply M_pair in H as [H|H]; apply (sing_pair H). 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)