proposition: Lemma oppr_ge0 x : (0 <= - x) = (x <= 0).
proof: Proof. by rewrite -sub0r subr_ge0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)