import tensorflow as tf

                               dtype=tf.float32)
      start_features = tf.einsum("lbh,bl->bh", output, start_index)
      start_features = tf.tile(start_features[None], [seq_len, 1, 1])
      end_logits = tf.layers.dense(
          tf.concat([output, start_features], axis=-1), xlnet_config.d_model,
          kernel_initializer=initializer, activation=tf.tanh, name="dense_0")
      end_logits = tf.contrib.layers.layer_norm(
          end_logits, begin_norm_axis=-1)
