input: 
  def common_elements(list1: List[int], list2: List[int]) -> List[int]:
      """Given two lists of integers, return a new list containing only the common elements between the two lists.
      >>> common_elements([1, 2, 3, 4, 8], [2, 6, 8, 10])
      [2, 8]
      >>> common_elements([5, 10, 15, 20], [4, 8, 20, 25])
      [20]
      """
  
output:     common_set = set(list1) & set(list2)
      return sorted(list(common_set))