(* OZ *)
intros; left; reflexivity.
(* pos n *)
intros; right; apply (tech_integ_posZ n b); exact H.
(* neg n *)
intros; right; apply (tech_integ_negZ n b); exact H.
Qed.

(************************)
Lemma tech_mult_pos_succZ :
forall n m : nat, posOZ (S n * S m) = multZ (pos n) (pos m).