input: Write a function to remove all duplicates from a provided list while preserving the original order of elements. If the list is empty, return an empty list.
  assert remove_duplicates([1, 3, 3, 5, 5, 7])==[1, 3, 5, 7]
  assert remove_duplicates([4, 4, 4, 4])==[4]
  assert remove_duplicates([1, 2, 3, 4, 5])==[1, 2, 3, 4, 5]
  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