proposition: Lemma rmorph_root p x : root p x -> root p^f (f x).
proof: Proof. by move/eqP=> px0; rewrite rootE horner_map px0 rmorph0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype bigop finset tuple) mathcomp(div ssralg countalg binomial)