proposition: Lemma ltNleif x y C : x <= y ?= iff ~~ C -> (x < y) = C.
proof: Proof. by move=> /lt_leif; rewrite negbK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)