// f: A -> Comparable
static <A> L<A> sortByCalculatedFieldDesc(Collection<A> c, final O f) {
  L<A> l = cloneList(c);
  sort(l, new Comparator<A>() {
    public int compare(A b, A a) {
      ret stdcompare(callF(f, a), callF(f, b));
    }
  });
  ret l;
}