proposition: Lemma in_shape_nil : in_shape [::] =1 pred0.
proof: Proof. by move=> [r c] /=; rewrite /in_shape /= nth_nil ltn0. Qed.
imports: HB(structures) mathcomp(all_ssreflect) mathcomp(div ssralg ssrint ssrnum binomial) tools combclass sorted ordtype