input: Write a function to find the union of two given lists. The function should return a set containing all the unique elements from both lists. If the lists are empty, the function should return an empty set.
  assert unionList([1, 2, 3, 4, 5], [3, 4, 5, 6, 7])=={1, 2, 3, 4, 5, 6, 7}
  assert unionList([], [])==set()
  assert unionList([1, 2, 3], [4, 5, 6])=={1, 2, 3, 4, 5, 6}
  assert unionList([1, 1, 1], [1, 1, 1])=={1}
  assert unionList([1, 2, 3], [])=={1, 2, 3}
output: def unionList(list1, list2):
      return set(list1).union(set(list2))