proposition: Lemma lteif_distl C x y e : (`|x - y| < e ?<= if C) = (y - e < x ?<= if C) && (x < y + e ?<= if C).
proof: Proof. by case: C; rewrite /= lter_distl. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)