proposition: Lemma union_intpartn_subproof : is_part_of_n (m + n) (merge geq l k).
proof: Proof. apply /andP; split. - by rewrite sumn_union_part !sumn_intpartn. - exact: merge_is_part. Qed.
imports: HB(structures) mathcomp(all_ssreflect) mathcomp(div ssralg ssrint ssrnum binomial) tools combclass sorted ordtype