From Undecidability.PCP.Reductions Require
SR_to_MPCP MPCP_to_MPCPb MPCP_to_PCP PCP_to_PCPb PCPb_iff_iPCPb PCPb_iff_dPCPb.
Require Undecidability.StringRewriting.SR_undec.
(** ** PCP is undecidable *)

(* The modified Post correspondence problem is undecidable. *)
Lemma MPCP_undec : undecidable MPCP.