proposition: Lemma commr_polyX p : GRing.comm p 'X.
proof: Proof. apply/polyP=> i; rewrite coefMr coefM. by apply: eq_bigr => j _; rewrite coefX commr_nat. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype bigop finset tuple) mathcomp(div ssralg countalg binomial)