proposition: Lemma oppr_le0 x : (- x <= 0) = (0 <= x).
proof: Proof. by rewrite lerNl oppr0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)