proposition: Lemma natr_indexg_neq0 G B : #|G : B|%:R != 0 :> R.
proof: Proof. by rewrite gt_eqF // natr_indexg_gt0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)