proposition: Lemma lteifxx x C : (x < x ?<= if C) = C.
proof: Proof. by case: C; rewrite /= ltexx. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)