proposition: Lemma lead_coefXn n : lead_coef 'X^n = 1.
proof: Proof. by rewrite /lead_coef nth_last polyseqXn last_rcons. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype bigop finset tuple) mathcomp(div ssralg countalg binomial)