proposition: Lemma precoeff_opp x s : precoeff x (prefreeg_opp s) = - precoeff x s.
proof: Proof. by rewrite !precoeffE prelift_opp. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop order generic_quotient) mathcomp(ssralg ssrnum ssrint)