proposition: Lemma mulNR x y : - x * y == - (x * y).
proof: Proof. by rewrite mulRC mulRN mulRC. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div order) mathcomp(ssralg ssrnum ssrint rat intdiv) Coq(Morphisms Setoid) fourcolor(real realsyntax)