intros Q p H'.
cut
(reduceplus A A0 A1 eqA invA minusA multA divA eqA_dec n ltM ltM_dec Q
(pO A n) p); [ intros Red1 | apply reducestar_reduceplus; auto ].
apply pO_reduceplus with (2 := Red1); auto.
Qed.

Theorem reducestar_pO_is_pO :
forall (Q : list (poly A0 eqA ltM)) (p q : list (Term A n)),
canonical A0 eqA ltM p -> reducestar Q (pO A n) (pO A n).