code: def attention_bias_proximal(length):
    
    r = tf.to_float(tf.range(length))
    diff = tf.expand_dims(r, 0) - tf.expand_dims(r, 1)
    return tf.expand_dims(tf.expand_dims(-tf.log1p(tf.abs(diff)), 0), 0)
docs: Bias for self-attention to encourage attention to close positions.
  
    Args:
      length: an integer scalar.
  
    Returns:
      a Tensor with shape [1, 1, length, length]