(* * PCP to CFPP *)
Hint Rewrite concat_app map_app map_map : list.
Hint Rewrite <- map_rev : list.
Definition gamma (A : stack nat) := map (fun '(x,y) => (x, rev y)) A.

Lemma tau2_gamma s A :
s el rev (tau2 (gamma A)) <-> s el tau2 A.