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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

async def series(self):
    '''list of series in the collection

    |force|

    |coro|

    Returns
    -------
    list
      of type :class:`embypy.objects.Series`
    '''
    items = []
    for i in await self.items:
      if i.type == 'Series':
        items.append(i)
      elif hasattr(i, 'series'):
        items.extend(await i.series)
    return items