proposition: Lemma comp_polyXr p : p \Po 'X = p.
proof: Proof. by rewrite -{2}/(idfun p) poly_initial. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype bigop finset tuple) mathcomp(div ssralg countalg binomial)