code: def d_grade_ipix(ipix, nside_in, nside_out, nest=False):
      
  
      if nside_in==nside_out: return ipix
      if not (nside_in > nside_out): 
          raise ValueError("nside_out must be less than nside_in")
  
      return hp.vec2pix(nside_out, *hp.pix2vec(nside_in, ipix, nest), nest=nest)
docs: Return the indices of the super-pixels which contain each of the
      sub-pixels (nside_in > nside_out).
  
      Parameters:
      -----------
      ipix      : index of the input subpixels
      nside_in  : nside of the input subpix
      nside_out : nside of the desired superpixels
  
      Returns:
      --------
      ipix_out  : superpixels for each subpixel