proposition: Lemma size_hookpartn d k : k < d -> size (hookpartn d k) = d - k.
proof: Proof. rewrite /hookpartn -lock /hookpart; case: d => //= d ltkd. by rewrite size_nseq subSn. Qed.
imports: HB(structures) mathcomp(all_ssreflect) mathcomp(div ssralg ssrint ssrnum binomial) tools combclass sorted ordtype