
theorem
  for V be non empty ModuleStr over INT.Ring, f, g be FrFunctional of V holds
  f+g = g+f
  proof
    let V be non empty ModuleStr over INT.Ring;
    let f, g be FrFunctional of V;
    now
      let x be Element of V;
      thus (f+g).x = f.x + g.x by HDef3
      .= (g+f).x by HDef3;
    end;
    hence thesis by FUNCT_2:63;
  end;
