proposition: Lemma freegU0 x : << 0 *g x >> = 0 :> {freeg K / R}.
proof: Proof. by apply/eqP/freeg_eqP=> y; rewrite coeffU coeff0 mul0r. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop order generic_quotient) mathcomp(ssralg ssrnum ssrint)