code: def get_internal_urls(self):
          
          internal_urls = self.get_subfields("856", "u", i1="4", i2="0")
          internal_urls.extend(self.get_subfields("998", "a"))
          internal_urls.extend(self.get_subfields("URL", "u"))
  
          return map(lambda x: x.replace("&amp;", "&"), internal_urls)
docs: URL's, which may point to edeposit, aleph, kramerius and so on.
  
          Fields ``856u40``, ``998a`` and ``URLu``.
  
          Returns:
              list: List of internal URLs.