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