reserve
  x, y for object,
  i, n for Nat,
  r, s for Real,
  f1, f2 for n-element real-valued FinSequence;

theorem Th3:
  for f, g being complex-valued Function holds abs(f-g) = abs(g-f)
  proof
    let f, g be complex-valued Function;
    f-g = -(g-f) by VALUED_2:18;
    hence thesis by EUCLID:5;
  end;
