proposition: Lemma ltr_distl x y e : (`|x - y| < e) = (y - e < x < y + e).
proof: Proof. exact: real_ltr_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)