proposition: Lemma poly_initial : pf =1 horner_morph poly_morphX_comm.
proof: Proof. apply: poly_ind => [|p a IHp]; first by rewrite !rmorph0. by rewrite !rmorphD !rmorphM /= -{}IHp horner_morphC ?horner_morphX. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype bigop finset tuple) mathcomp(div ssralg countalg binomial)