proposition: Lemma le_succ_succ x y: x <= y -> T2succ x <= T2succ y.
proof: Proof. rewrite !T2leNgt; apply: contra; exact:lt_succ_succ. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(fintype bigop)