proposition: Lemma le_succ_succ x y: x <= y -> T3succ x <= T3succ y.
proof: Proof. rewrite !T3leNgt; apply: contra; exact:lt_succ_succ. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(fintype bigop)