theorem BLTh20:
  for V, W being non empty ModuleStr over INT.Ring, f being Functional of V,
  v being Vector of V, w being Vector of W holds
  FormFunctional(f,0Functional(W)).(v,w) = 0
  proof
    let V, W be non empty ModuleStr over INT.Ring;
    let f be Functional of V, v be Vector of V, y be Vector of W;
    set 0F = 0Functional(W), F = FormFunctional(f,0F);
    thus F.(v,y) = f.v * 0F.y by BLDef10
    .= f.v * 0
    .= 0;
  end;
