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