proposition: Lemma lead_coefXsubC a : lead_coef ('X - a%:P) = 1.
proof: Proof. by rewrite lead_coefE polyseqXsubC. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype bigop finset tuple) mathcomp(div ssralg countalg binomial)