proposition: Lemma polyOverX : 'X \in polyOver S.
proof: Proof. by rewrite qualifE /= polyseqX /= rpred0 rpred1. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype bigop finset tuple) mathcomp(div ssralg countalg binomial)