input: Write a function to remove all duplicate elements from a list while preserving the original order. If the input list is empty, return an empty list.
  def remove_duplicates(nums):
   new_list = []
   for num in nums:
   if num not in new_list:
   new_list.append(num)
   
  return new_list
  
  assert remove_duplicates([1, 3, 3, 5, 5, 7])==[1, 3, 5, 7]
  assert remove_duplicates([2, 4, 4, 2, 6])==[2, 4, 6]
  assert remove_duplicates([])==[]
  assert remove_duplicates([1, 1, 1, 1])==[1]
  assert remove_duplicates([7, 8, 9, 9, 8, 7])==[7, 8, 9]
output: def remove_duplicates(nums):
      new_list = []
      for num in nums:
          if num not in new_list:
              new_list.append(num)
      return new_list