input: Write a function to remove duplicates from a list. The function should return a new list with all duplicate elements removed while maintaining the order of the first occurrence of each element. If the input list is empty, the function should return an empty list.
  assert remove_duplicates([1, 2, 3, 4, 3, 2, 1])==[1, 2, 3, 4]
  assert remove_duplicates([5, 6, 7, 7, 6, 5])==[5, 6, 7]
  assert remove_duplicates([8, 9, 10])==[8, 9, 10]
  assert remove_duplicates([])==[]
output: def remove_duplicates(lst):
      seen = set()
      result = []
      for item in lst:
          if item not in seen:
              seen.add(item)
              result.append(item)
      return result