proposition: Lemma ler_ndivrMl z x y : z < 0 -> (z^-1 * y <= x) = (z * x <= y).
proof: Proof. by move=> z_lt0; rewrite mulrC ler_ndivrMr ?[z * _]mulrC. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)