proposition: Lemma le_sig : {mono sig : i j / i <= j}.
proof: Proof. by move=> i j; rewrite /sig/= le_enum_val//; apply: le_total. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)