proposition: Lemma dmuleDl x y z : x \is a fin_num -> y +? z -> (y + z) * x = y * x + z * x.
proof: Proof. by move=> *; rewrite -!(muleC x) dmuleDr. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap) mathcomp(mathcomp_extra) signed