proposition: Lemma sigma_el x y : x ∈ σ y <-> x ∈ y \/ x = y.
proof: Proof. Proof using M_FST VIEQ. rewrite M_adj. tauto. Qed.
imports: Undecidability.FOL(Syntax.Facts Semantics.Tarski.FullFacts FST) Undecidability.FOL(Sets.FST) Undecidability.FOL.TRAKHTENBROT(hfs) Undecidability.Shared.Libs.DLW.Utils(finite) Undecidability(Shared.ListAutomation) Coq(Lia)