input: from typing import List
  
  def union_of_lists(list1: List[int], list2: List[int]) -> List[int]:
      """Finds the union of two lists.
      
      >>> union_of_lists([1, 2, 3, 4, 5], [3, 4, 5, 6, 7])
      [1, 2, 3, 4, 5, 6, 7]
      """
      return sorted(list(set(list1 + list2)))
output:     union_set = set(list1).union(set(list2))
      return sorted(list(union_set))