input: Write a python function to find the intersection of two lists and return it as a set.
  assert find_intersection([2, 3, 4], [3, 5, 6, 4]) == {3, 4}
  assert find_intersection([1, 2, 3], [4, 5, 6]) == set()
  assert find_intersection([7, 8, 9], [9, 10, 11]) == {9}
output: def find_intersection(list1, list2):
      return set(list1) & set(list2)