docs: def load_model():
      """
      Load a n-gram language model for mathematics in ARPA format which gets
      shipped with hwrt.
  
      Returns
      -------
      A NgramLanguageModel object
      """
      logging.info("Load language model...")
      ngram_arpa_t = pkg_resources.resource_filename('hwrt',
                                                     'misc/ngram.arpa.tar.bz2')
      with tarfile.open(ngram_arpa_t, 'r:bz2') as tar:
          tarfolder = tempfile.mkdtemp()
          tar.extractall(path=tarfolder)
      ngram_arpa_f = os.path.join(tarfolder, 'ngram.arpa')
      with open(ngram_arpa_f) as f:
          content = f.read()
      ngram_model = NgramLanguageModel()
      ngram_model.load_from_arpa_str(content)
      return ngram_model