theorem BLTh21:
  for V, W being non empty ModuleStr over INT.Ring, g being Functional of W,
  v being Vector of V, w be Vector of W holds
  FormFunctional(0Functional(V),g).(v,w) = 0
proof
  let V, W be non empty ModuleStr over INT.Ring;
  let h be Functional of W, v be Vector of V, y be Vector of W;
  set 0F = 0Functional(V), F = FormFunctional(0F,h);
  thus F.(v,y) = 0F.v * h.y by BLDef10
    .= 0 * h.y
    .= 0;
end;
