code: def default_freq(**indexer):
      
      freq = 'AS-JAN'
      if indexer:
          if 'DJF' in indexer.values():
              freq = 'AS-DEC'
          if 'month' in indexer and sorted(indexer.values()) != indexer.values():
              raise (NotImplementedError)
  
      return freq
docs: Return the default frequency.