code: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import os
  
  import tensorflow as tf
  from tensorflow.python import pywrap_tensorflow
  
  cur_dir = os.path.dirname(os.path.realpath(__file__))
  
  coref_op_library = tf.load_op_library(os.path.join(cur_dir, "coref_kernels.so"))
  
  extract_spans = coref_op_library.extract_spans
  tf.NotDifferentiable("ExtractSpans")
  
apis: tensorflow.NotDifferentiable