theorem
  -H = (-1)(#)H
  proof
    now
      let n be Element of NAT;
      thus (-H).n = -H.n by Def3
      .= (-1)(#)(H.n) by VFUNCT_1:23
      .=((-1)(#)H).n by Def1;
    end;
    hence thesis by FUNCT_2:63;
  end;
