proposition: Lemma coefXM p i : ('X * p)`_i = (if (i == 0)%N then 0 else p`_i.-1).
proof: Proof. by rewrite -commr_polyX coefMX. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype bigop finset tuple) mathcomp(div ssralg countalg binomial)