proposition: Lemma binunion_eset x : x ≡' ∅ ∪ x.
proof: Proof. Proof using M_ZF. apply M_ext. - intros y H. apply binunion_el. now right. - intros y [H|H] % binunion_el. + now apply M_eset in H. + assumption. Qed.
imports: Undecidability.FOL.ZF Undecidability.FOL.Syntax.Facts Undecidability.FOL.Semantics.Tarski.FullFacts Undecidability.FOL.Sets(ZF) Undecidability.FOL.Sets.ZF Undecidability.FOL.Reductions.PCPb_to_ZF Lia Undecidability.PCP(PCP Util.PCP_facts Reductions.PCPb_iff_dPCPb) Undecidability(Shared.ListAutomation) Morphisms