proposition: Lemma lerNl x y : (- x <= y) = (- y <= x).
proof: Proof. by rewrite (monoLR opprK lerN2). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)