proposition: Lemma ltBRight_leBLeft b x : b < BRight x = (b <= BLeft x).
proof: Proof. by move: b => [[] b|[]]. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(div fintype bigop order ssralg finset fingroup) mathcomp(ssrnum)