static L<TripleWeb> ai_sort_topRelationsFirst(L<TripleWeb> l) {
  final Set<S> topRelations = ai_topRelationsSet();
  ret sorted(l, new Comparator<TripleWeb> {
    public int compare(TripleWeb a, TripleWeb b) {
      ret -boolDiff(topRelations.contains(a.b), topRelations.contains(b.b));
    }
  });
}