reserve D for non empty set,
  D1, D2, x, y, Z for set,
  n, k for Nat,
  p, x1, r for Real,
  f for Function,
  Y for RealNormSpace,
  G, H, H1, H2, J for Functional_Sequence of D,the carrier of Y;

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;
