proposition: Lemma sing_el x y : x ∈ M_sing y <-> x = y.
proof: Proof. Proof using M_FST VIEQ. split. - now intros [H|H] % M_pair. - intros ->. apply M_pair. now left. 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)