proposition: Lemma pi_fgopp : {morph \pi : D / fgopp_r D >-> fgopp D}.
proof: Proof. case=> [D redD]; unlock fgopp; rewrite ?piE. apply/eqmodP/freegequivP => k /=. by rewrite !precoeff_reduce !precoeff_opp !precoeff_repr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop order generic_quotient) mathcomp(ssralg ssrnum ssrint)