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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 heightmap_add_hm( hm1: np.ndarray, hm2: np.ndarray, hm3: np.ndarray ) -> None: """Add two heightmaps together and stores the result in ``hm3``. Args: hm1 (numpy.ndarray):
 The first heightmap. hm2 (numpy.ndarray):
 The second heightmap to add to the first. hm3 (numpy.ndarray):
 A destination heightmap to store the result. .. deprecated:: 2.0 Do ``hm3[:] = hm1[:] + hm2[:]`` instead. """

    hm3[:] = hm1[:] + hm2[:]