static <B, C, A extends Map<B, C>> L<A> sortByMapKey(Iterable<A> c, B key) {
  L<A> l = cloneList(c);
  sort(l, new Comparator<A>() {
    public int compare(A a, A b) {
      ret stdcompare(mapGet(a, key), mapGet(b, key));
    }
  });
  ret l;
}