proposition: Lemma fmorph_root p x : root p^f (f x) = root p x.
proof: Proof. by rewrite rootE horner_map // fmorph_eq0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype bigop finset tuple) mathcomp(div ssralg countalg binomial)