input: Write a function that takes two sets of integers as input and outputs the intersection of those sets. If one of the sets is empty, return the empty set. If both sets are empty, return the 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(), {1, 2, 3})==set()
  assert intersection(set(), set())==set()
output: def intersection(set1, set2):
      if not set1 or not set2:
          return set()
      return set1 & set2