proposition: Lemma nbsurj_SSnn n: nbsurj n.+2 n = ('C(n.+3,4) + 2 * 'C(n.+2,4)) * n`!.
proof: Proof. by rewrite /nbsurj stir_SSnn. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype) mathcomp(ssrnat seq path div) mathcomp(fintype tuple finfun bigop finset binomial)