(** Warning! (-0) won't parse (compatibility with the behavior of Z). *)

(* Specifications: *)
Lemma isi_negnil :
int_of_string (string_of_int (Neg Nil)) = Some (Neg (D0 Nil)).
Lemma sis s d :
int_of_string s = Some d -> string_of_int d = s.
Lemma isi_negnil :
int_of_string (string_of_int (Neg Nil)) = Some (Neg (D0 Nil)).
Lemma sis s d :
int_of_string s = Some d -> string_of_int d = s.