input: Write a function to find the intersection of two sets of integers. If either set is empty, return an empty set.
  assert intersection({1, 2, 3, 4}, {3, 4, 5, 6}) == {3, 4}
  assert intersection({1, 2, 3}, {4, 5, 6}) == set()
  assert intersection(set(), {3, 4, 5, 6}) == set()
  assert intersection({1, 2, 3, 4}, set()) == set()
  assert intersection(set(), set()) == set()
output: def intersection(set1, set2):
      if not set1 or not set2:
          return set()
      return set1 & set2