proposition: Lemma freeg_cat (s1 s2 : seq (R * K)) : [freeg s1 ++ s2] = [freeg s1] + [freeg s2].
proof: Proof. by apply/eqP/freeg_eqP => k; rewrite coeffD !coeff_Freeg precoeff_cat. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop order generic_quotient) mathcomp(ssralg ssrnum ssrint)