code: def get_cited_dois(arxiv_id):
      
      dois = {}
      # Get the list of bbl files for this preprint
      bbl_files = arxiv.get_bbl(arxiv_id)
      for bbl_file in bbl_files:
          # Fetch the cited DOIs for each of the bbl files
          dois.update(bbl.get_cited_dois(bbl_file))
      return dois
docs: Get the DOIs of the papers cited in a .bbl file.
  
      .. note::
  
          Bulk download of sources from arXiv is not permitted by their API. \
                  You should have a look at http://arxiv.org/help/bulk_data_s3.
  
      :param arxiv_id: The arXiv id (e.g. ``1401.2910`` or ``1401.2910v1``) in \
              a canonical form.
      :returns: A dict of cleaned plaintext citations and their associated DOI.