input: 
  def remove_duplicates(nums):
      new_list = []
      for num in nums:
          if num not in new_list:
              new_list.append(num)
      return new_list
  
  # Test cases
  """
  >>> remove_duplicates([1, 3, 3, 5, 5, 7])
  [1, 3, 5, 7]
  >>> remove_duplicates([2, 2, 2, 2])
  [2]
  >>> remove_duplicates([])
  []
  >>> remove_duplicates([1, 2, 3, 4])
  [1, 2, 3, 4]
  """
  
output:     return new_list