proposition: Lemma behead_hookpartn d k : behead (hookpartn d k) = nseq (d.-1 - k) 1%N.
proof: Proof. by rewrite /hookpartn -lock /hookpart; case: d => [|d]. Qed.
imports: HB(structures) mathcomp(all_ssreflect) mathcomp(div ssralg ssrint ssrnum binomial) tools combclass sorted ordtype