(** * Some results about the sign function. *)
Notation Zsgn_Zmult := Z.sgn_mul (only parsing).
Notation Zsgn_Zopp := Z.sgn_opp (only parsing).
Notation Zsgn_pos := Z.sgn_pos_iff (only parsing).
Notation Zsgn_neg := Z.sgn_neg_iff (only parsing).
Notation Zsgn_null := Z.sgn_null_iff (only parsing).
(** A characterization of the sign function: *)

(* Specifications: *)
Lemma Zsgn_spec x :
0 < x /\ Z.sgn x = 1 \/
0 = x /\ Z.sgn x = 0 \/
0 > x /\ Z.sgn x = -1.