proposition: Lemma sigK : cancel sig rank.
proof: Proof. by move=> s; rewrite /sig/rank/= enum_valK cast_ord_comp cast_ord_id. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)