input: Write a function that removes duplicates from a given list and maintains the order of the remaining elements.
  
  def remove_duplicates(my_list):
      return list(dict.fromkeys(my_list))
  
  assert remove_duplicates([1, 2, 3, 4, 3, 2, 1]) == [1, 2, 3, 4]
  assert remove_duplicates([5, 6, 7, 6, 5, 8]) == [5, 6, 7, 8]
  assert remove_duplicates([]) == []
  assert remove_duplicates([1, 1, 1, 1]) == [1]
output: def remove_duplicates(my_list):
      seen = set()
      result = []
      for item in my_list:
          if item not in seen:
              seen.add(item)
              result.append(item)
      return result