unfold is_unitary_commutative_ring in |- *.
split. exact Z_ring.
split. exact multZ_commutativity. exact multZ_neutral.
Qed.

(* Z is an integral domain *)
(********************)
Lemma tech_integ_posZ :
forall (n : nat) (x : Z), multZ (pos n) x = OZ -> x = OZ.