def METHOD_NAME(self, snapnum):
    """Get the internal consistent-trees ids for each original halo-finder ID"""
    this_snap_mask = (self._snap_nums == snapnum)
    internal_ids_this_snap = self.links['id_this'][this_snap_mask]
    finder_ids_this_snap = self._id_to_finder_id[internal_ids_this_snap]
    finder_id_to_id = dict(zip(finder_ids_this_snap, internal_ids_this_snap))
    return finder_id_to_id