proposition: Lemma stir_Snn' n: 'St(n.+1, n) = \sum_(i<n.+1) i.
proof: Proof. elim: n => [//| n Ihn]; first by rewrite big_ord_recl big_ord0. by rewrite big_ord_recr /= stirS Ihn stir_nn addnC muln1. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype) mathcomp(ssrnat seq path div) mathcomp(fintype tuple finfun bigop finset binomial)