docs: def ud_grade_ipix(ipix, nside_in, nside_out, nest=False):
      """
      Upgrade or degrade resolution of a pixel list.
  
      Parameters:
      -----------
      ipix:array-like 
      the input pixel(s)
  
      nside_in:int
      the nside of the input pixel(s)
  
      nside_out:int
      the desired nside of the output pixel(s)
  
      order:str
      pixel ordering of input and output ("RING" or "NESTED")
  
      Returns:
      --------
      pix_out:array-like
      the upgraded or degraded pixel array
      """
      if nside_in == nside_out: return ipix
      elif nside_in < nside_out:
          return u_grade_ipix(ipix, nside_in, nside_out, nest)
      elif nside_in > nside_out:
          return d_grade_ipix(ipix, nside_in, nside_out, nest)