(** ** Boolean operations on [RegExp] are morphism. *)
(** [Or] corresponds to plus in Kleene algebra. *)
Add Parametric Morphism : And with
signature re_eq ==> re_eq ==> re_eq as And_morphism.
Add Parametric Morphism : Not with
signature re_eq ==> re_eq as Not_morphism.
(** [matches] is a homomorphism from [RegExp] to bool for [And], [Or], and [Not]. *)

Lemma Or_assoc_s : forall s r r' r'',
((r || r') || r'') ~= s = (r || (r' || r'')) ~= s.