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