fact: Definition P := [d ; e] ++ R ++ [ ([#] / [#] )] ++ map (fun a => [a] / [a]) Sigma.
imports: List Undecidability.PCP.PCP Undecidability.PCP.Util.Facts Undecidability.PCP.Util.PCP_facts Undecidability.StringRewriting.SR Undecidability.StringRewriting.Util.Definitions Undecidability.Synthetic.Definitions