input: Write a function to remove all duplicate elements from a given list while preserving the original order. The function should take a list as input and return a new list with all duplicate elements removed.
  assert remove_duplicates([1, 3, 3, 5, 5, 7]) == [1, 3, 5, 7]
  assert remove_duplicates([2, 2, 2, 2]) == [2]
  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