code: def ordered_plane_redshifts_from_galaxies(galaxies):
      
      ordered_galaxies = sorted(galaxies, key=lambda galaxy: galaxy.redshift, reverse=False)
  
      # Ideally we'd extract the planes_red_Shfit order from the list above. However, I dont know how to extract it
      # Using a list of class attributes so make a list of redshifts for now.
  
      galaxy_redshifts = list(map(lambda galaxy: galaxy.redshift, ordered_galaxies))
      return [redshift for i, redshift in enumerate(galaxy_redshifts) if redshift not in galaxy_redshifts[:i]]
docs: Given a list of galaxies (with redshifts), return a list of the redshifts in ascending order.
  
      If two or more galaxies have the same redshift that redshift is not double counted.
  
      Parameters
      -----------
      galaxies : [Galaxy]
          The list of galaxies in the ray-tracing calculation.