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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 _remove_hidden_parts(projected_surface):
 """Removes parts of a projected surface that are not visible. Args: projected_surface (surface):
 the surface to use Returns: surface: A projected surface. """

    surface = np.copy(projected_surface)
    surface[~_make_occlusion_mask(projected_surface)] = np.nan
    return surface