input: Write a function to return the intersection of two sets of integers. If both sets are empty, it should return an empty set.
  assert intersection({1, 2, 3, 4}, {3, 4, 5, 6})=={3, 4}
  assert intersection({5, 6, 7}, {8, 9, 10})==set()
  assert intersection({1, 2, 3}, {2, 3, 4})=={2, 3}
  assert intersection({}, {3, 4, 5})==set()
  assert intersection({}, {})==set()
output: def intersection(set1, set2):
      return set1 & set2