proposition: Lemma map_polyX : ('X)^f = 'X.
proof: Proof. by apply/polyP=> i; rewrite coef_map !coefX /= rmorph_nat. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype bigop finset tuple) mathcomp(div ssralg countalg binomial)