code: def galaxies_in_redshift_ordered_planes_from_galaxies(galaxies, plane_redshifts):
      
  
      galaxies_in_redshift_ordered_planes =  [[] for i in range(len(plane_redshifts))]
  
      for galaxy in galaxies:
  
          index = (np.abs(np.asarray(plane_redshifts) - galaxy.redshift)).argmin()
  
          galaxies_in_redshift_ordered_planes[index].append(galaxy)
  
      return galaxies_in_redshift_ordered_planes
docs: Given a list of galaxies (with redshifts), return a list of the galaxies where each entry contains a list \
      of galaxies at the same redshift in ascending redshift order.
  
      Parameters
      -----------
      galaxies : [Galaxy]
          The list of galaxies in the ray-tracing calculation.