proposition: Lemma leR_opp2 x y : - x <= - y <-> y <= x.
proof: Proof. by rewrite -subR_ge0 oppRK addRC subR_ge0. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div order) mathcomp(ssralg ssrnum ssrint rat intdiv) Coq(Morphisms Setoid) fourcolor(real realsyntax)