input: Write a function to remove all duplicate elements from a list while preserving the original order. The function should take a list of integers as input and return a new list with all duplicates removed. If the input list is empty, the function should 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([2, 3, 4, 2, 3])==[2, 3, 4]
  assert remove_duplicates([])==[]
output: def remove_duplicates(lst):
      seen = set()
      result = []
      for num in lst:
          if num not in seen:
              seen.add(num)
              result.append(num)
      return result