code: def get_plaintext_citations(arxiv_id):
      
      plaintext_citations = []
      # 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
          plaintext_citations.extend(bbl.get_plaintext_citations(bbl_file))
      return plaintext_citations
docs: Get the citations of a given preprint, in plain text.
  
      .. 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 list of cleaned plaintext citations.