proposition: Lemma mulRN x y : x * - y == - (x * y).
proof: Proof. by apply (@addRI (x * y)); rewrite -mulRDr !subRR mulR0. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div order) mathcomp(ssralg ssrnum ssrint rat intdiv) Coq(Morphisms Setoid) fourcolor(real realsyntax)