proposition: Lemma poly_morphX_comm : commr_rmorph (pf \o polyC) (pf 'X).
proof: Proof. by move=> a; rewrite /GRing.comm /= -!rmorphM // commr_polyX. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype bigop finset tuple) mathcomp(div ssralg countalg binomial)