proposition: Lemma Tnk2_Snn n: Tnk2 n.+1 n = n.*2.+1.
proof: Proof. by rewrite /Tnk2 -{2}add1n addnK bin1 -addnA addn1 addnn mulKn. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype) mathcomp(ssrnat seq path div) mathcomp(fintype tuple finfun bigop finset binomial)