input: Write a python function to swap two numbers without using a temporary variable.
  assert swap_numbers(3, 5) == (5, 3)
  assert swap_numbers(10, -2) == (-2, 10)
  assert swap_numbers(0, 1) == (1, 0)
output: def swap_numbers(a, b):
      a = a + b
      b = a - b
      a = a - b
      return a, b