(** Same as [index] but with no optional type, we return [0] when it
    does not occur *)

Definition findex n s1 s2 :=
  match index n s1 s2 with
  | Some n => n
  | None => O
  end.(** *** Conversion to/from [list ascii] and [list byte] *)

Fixpoint string_of_list_ascii (s : list ascii) : string
  := match s with
     | nil => EmptyString
     | cons ch s => String ch (string_of_list_ascii s)
     end.Fixpoint list_ascii_of_string (s : string) : list ascii
  := match s with
     | EmptyString => nil
     | String ch s => cons ch (list_ascii_of_string s)
     end.

Lemma list_ascii_of_string_of_list_ascii s : list_ascii_of_string (string_of_list_ascii s) = s.