proposition: Lemma leR_opp2 x y : x <= y -> - y <= - x.
proof: Proof. by move=> lexy a [b ltab ltyb]; exists b => // /lexy. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq order) mathcomp(ssralg ssrnum ssrint rat) fourcolor(real) Coq(Setoid Morphisms)