intros q H'; inversion H'; auto.
intros a l H' q H'0; inversion H'0; auto.
Qed.
Hint Resolve eqp_refl.

(* Specifications: *)
Theorem pO_plusP_inv2 : forall p q, plusP p (pO A n) q -> p = q.
intros p; elim p.
Theorem plusP_decomp :
forall a p,
canonical A0 eqA ltM (pX a p) -> plusP (pX a (pO A n)) p (pX a p).