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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def attention_bias_proximal(length):
 """Bias for self-attention to encourage attention to close positions. Args: length: an integer scalar. Returns: a Tensor with shape [1, 1, length, 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)