code: def write_conll(docgraph, output_file, coreference_layer=None,
                  markable_layer=None):
      
      if markable_layer is None:
          markable_layer = docgraph.ns+':markable'
      conll_file = Conll2009File(docgraph,
                                 coreference_layer=coreference_layer,
                                 markable_layer=markable_layer)
      assert isinstance(output_file, (str, file))
      if isinstance(output_file, str):
          path_to_file = os.path.dirname(output_file)
          if not os.path.isdir(path_to_file):
              create_dir(path_to_file)
          conll_file.write(output_file)
      else:  # output_file is a file object
          output_file.write(conll_file.__str__())
docs: converts a DiscourseDocumentGraph into a tab-separated CoNLL 2009 file and
      writes it to the given file (or file path).