(** * PCP to CFP *)
Section PCP_CFP.
Variable P : SRS.
Definition Sigma := sym P.
Notation "#" := (fresh Sigma).
Definition gamma (A : SRS) := map (fun '(x,y) => (x, rev y)) A.

Lemma sigma_gamma a A :
sigma a (gamma A) = tau1 A ++ a ++ rev (tau2 A).