theorem
  for V being LeftMod of INT.Ring, a being Element of INT.Ring,
      v being Vector of V holds
    (- a) * v = - a * v
  proof
    let V be LeftMod of INT.Ring,
        a be Element of INT.Ring,
        v be Vector of V;
    thus (- a) * v = a * (- v) by Th5
    .= - a * v by Th6;
  end;
