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