proposition: Lemma eq_equiv x y : x ≈ y <-> x ≡ y.
proof: Proof. Proof using M_ZF. split. - intros H. apply sing_el; trivial. apply H. apply sing_el; trivial. now apply set_equiv_equiv. - intros H z. apply set_equiv_elem; trivial. now apply set_equiv_equiv. Qed.
imports: Undecidability.FOL.Syntax.Facts Undecidability.FOL.Syntax.Asimpl Undecidability.FOL.Semantics.Tarski.FullFacts Undecidability.FOL.Deduction.FullNDFacts Undecidability.FOL.Sets(binZF ZF) Undecidability.FOL.Reductions.PCPb_to_ZF Undecidability(Shared.ListAutomation) Morphisms Undecidability.FOL(Reductions.PCPb_to_ZFeq)