theorem Th2:
  for seq be sequence of S holds -seq=(-1)*seq
proof
  let seq be sequence of S;
  now
    let n be Element of NAT;
    thus ((-1)*seq).n =(-1)*seq.n by NORMSP_1:def 5
      .=-seq.n by RLVECT_1:16
      .=(-seq).n by BHSP_1:44;
  end;
  hence thesis by FUNCT_2:63;
end;
