proposition: Lemma polyseqXn n : 'X^n = rcons (nseq n 0) 1 :> seq R.
proof: Proof. elim: n => [|n IHn]; rewrite ?polyseq1 // exprSr. by rewrite polyseqMX -?size_poly_eq0 IHn ?size_rcons. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype bigop finset tuple) mathcomp(div ssralg countalg binomial)