(** * Coq codes *)
(** ** Dependencies *)
Require Export Ascii.
Require Export String.
Require Export List.
Require Export Relation_Definitions.
(** ** Equality and equivalence *)
Definition bool_eq (a a':bool) : Prop := a = a'.
Definition ascii_eq (a a':ascii) : Prop := a = a'.
Definition string_eq (a a':string) : Prop := a = a'.
(** ** Lemmas for string *)

Lemma string_assoc : forall s s' s'':string,
((s ++ s') ++ s'')%string = (s ++ (s' ++ s''))%string.