intros l1 l2 H' H'0; generalize (pluspf_is_plusP l1 l2); intros u1.
apply canonical_plusP with (l1 := l1) (l2 := l2); auto.
Qed.

Theorem pO_plusP_inv1 : forall p q, plusP (pO A n) p q -> p = q.
intros p; elim p.