proposition: Lemma tau1_inv (a : nat) B z : tau1 B = a :: z -> exists x y, (a :: x, y) el B.
proof: Proof. induction B; cbn; intros; inv H. destruct a0 as ([],y). - cbn in H1. firstorder. - cbn in H1. inv H1. eauto. Qed.
imports: List Undecidability.PCP.PCP Undecidability.PCP.Util.Facts Undecidability.Synthetic(Definitions DecidabilityFacts EnumerabilityFacts MoreEnumerabilityFacts ListEnumerabilityFacts) Coq.Init.Wf Undecidability.Shared.Libs.DLW.Utils(utils_tac utils_list utils_nat finite)