proposition: Lemma tau2_cards {X : Type} (x: list X) : tau2 (cards x) = x.
proof: Proof. induction x; cbv in *; try rewrite IHx; trivial. 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)