unfold not in |- *; simpl in |- *; intros; exact H.
unfold not in |- *; simpl in |- *; intros; exact H.
unfold not in |- *; simpl in |- *; intros; exact H.
Qed.

(**********)
Lemma Zrec1 :
forall P : Z -> Set,
(forall n : Z, (forall m : Z, lt_absZ m n -> P m) -> P n) -> P OZ.