(** * Coq codes *)
(** ** Dependencies *)
Require Export RegExp.Utility.
Require Export RegExp.Definitions.
Require Export RegExp.Boolean.
(** ** [Cat] is morphism *)

(* Specifications: *)
Lemma Cat_morphism_s : forall s r0 r1 r0' r1',
r0 =R= r1 -> r0' =R= r1' -> (r0 ++ r0') ~= s = (r1 ++ r1') ~= s.