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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 flatten4d3d(x):
 """Flatten a 4d-tensor into a 3d-tensor by joining width and height."""

  xshape = shape_list(x)
  result = tf.reshape(x, [xshape[0], xshape[1] * xshape[2], xshape[3]])
  return result