proposition: Lemma M_union x y : x ∈ ⋃ y <-> exists z, z ∈ y /\ x ∈ z.
proof: Proof. Proof using M_ZF VIEQ. apply (@M_ZF (fun _ => ∅) ax_union). cbn; tauto. Qed.
imports: Undecidability.FOL(Syntax.Facts Semantics.Tarski.FullFacts) Undecidability.FOL(Sets.ZF) Undecidability.FOL(ZF) Undecidability.FOL.TRAKHTENBROT(hfs) Undecidability.Shared.Libs.DLW.Utils(finite) Undecidability(Shared.ListAutomation) Lia