theorem
  for V, W being non empty ModuleStr over INT.Ring,
      a, b being Element of INT.Ring,
  f being Form of V,W holds (a*b)*f = a*(b*f)
  proof
    let V, W be non empty ModuleStr over INT.Ring,
        r, s be Element of INT.Ring,
        f be Form of V,W;
    now
      let v be Vector of V, w be Vector of W;
      thus ((r*s)*f).(v,w) = (r*s) * f.(v,w) by BLDef3
      .= r*(s*f.(v,w))
      .= r*(s*f).(v,w) by BLDef3
      .= (r*(s*f)).(v,w) by BLDef3;
  end;
  hence thesis;
end;
