proposition: Lemma comm_polyM p q x: comm_poly p x -> comm_poly q x -> comm_poly (p * q) x.
proof: Proof. by move=> px qx; rewrite /comm_poly hornerM_comm// mulrA px -mulrA qx mulrA. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype bigop finset tuple) mathcomp(div ssralg countalg binomial)