proposition: Lemma gec0_opp x : x < 0 -> - x >= 0.
proof: Proof. by move=> ltx0 [a lt0a []]; apply: ltc_trans lt0a; rewrite oppr0. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq order) mathcomp(ssralg ssrnum ssrint rat) fourcolor(real) Coq(Setoid Morphisms)