code: def is_monotonic(full_list):
      
      prev_elements = set({full_list[0]})
      prev_item = full_list[0]
  
      for item in full_list:
          if item != prev_item:
              if item in prev_elements:
                  return False
              prev_item = item
              prev_elements.add(item)
  
      return True
docs: Determine whether elements in a list are monotonic. ie. unique
      elements are clustered together.
  
      ie. [5,5,3,4] is, [5,3,5] is not.