input: Write a python function to find the set difference between two sets.
  assert set_difference({1, 2, 3, 4}, {2, 3}) == {1, 4}
  assert set_difference({5, 6, 7}, {6, 8}) == {5, 7}
  assert set_difference({10, 20, 30}, {20, 40, 50}) == {10, 30}
output: def set_difference(set1, set2):
      return set1 - set2