proposition: Lemma ler_norml x y : (`|x| <= y) = (- y <= x <= y).
proof: Proof. exact: real_ler_norml. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)