(* Contribution to the Coq Library   V6.3 (July 1999)                    *)
Definition leZ (x y : Z) :=
match x return Prop with
| OZ =>
match y return Prop with
| OZ => True
| pos n => True
| neg n => False
end
| pos n =>
match y return Prop with
| OZ => False
| pos m => n <= m
| neg m => False
end
| neg n =>
match y return Prop with
| OZ => True
| pos m => True
| neg m => m <= n
end
end.
intros; elim x; simpl in |- *.
exact I.
intro; simpl in |- *.
exact I.
intro; simpl in |- *.
exact I.
Qed.
intro x; elim x.
unfold absZ in |- *; reflexivity.
unfold absZ in |- *; reflexivity.
intros; elim H.
Qed.

Theorem leZ_antisymmetric : forall x y : Z, leZ x y -> leZ y x -> x = y.