proposition: Lemma nbsurj_Snn n: 'Sj(n.+1, n) = 'C(n.+1,2) * n`!.
proof: Proof. by rewrite /nbsurj stir_Snn. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype) mathcomp(ssrnat seq path div) mathcomp(fintype tuple finfun bigop finset binomial)