proposition: Lemma perm_eq_fgrepr rD : perm_eq (repr (\pi_freeg rD)) rD.
proof: Proof. by rewrite -/(fgequiv _ _); apply/eqmodP; rewrite reprK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop order generic_quotient) mathcomp(ssralg ssrnum ssrint)