proposition: Lemma predeg_perm_eq D1 D2 : perm_eq D1 D2 -> predeg D1 = predeg D2.
proof: Proof. by rewrite !predegE => /prelift_perm_eq ->. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop order generic_quotient) mathcomp(ssralg ssrnum ssrint)