proposition: Lemma part_head0F sh : head 1 sh == 0 -> is_part sh = false.
proof: Proof. elim: sh => //= sh0 sh IHsh /eqP->. by rewrite leqn0; case (boolP (head 1 sh == 0)). Qed.
imports: HB(structures) mathcomp(all_ssreflect) mathcomp(div ssralg ssrint ssrnum binomial) tools combclass sorted ordtype