proposition: Lemma contra_ltF b x y : (b -> x <= y) -> (y < x -> b = false).
proof: Proof. by case: comparableP; case: b => // _ /implyP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)