input: Write a python function to find the intersection of two sets.
  assert intersection({1, 2, 3}, {2, 3, 4}) == {2, 3}
  assert intersection({5, 6, 7}, {7, 8, 9}) == {7}
  assert intersection({10, 20, 30}, {40, 50, 60}) == set()
output: def intersection(set1, set2):
      return set1 & set2