proposition: Lemma pmulR_rle0 x y : x > 0 -> (x * y <= 0 <-> y <= 0).
proof: Proof. by move=> x_gt0; rewrite -(leR_pmul2l y 0 x_gt0) mulR0. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div order) mathcomp(ssralg ssrnum ssrint rat intdiv) Coq(Morphisms Setoid) fourcolor(real realsyntax)