static Comparator makeReversedComparator(O f) {
  ret new Comparator {
    public int compare(O a, O b) {
      ret (int) callF(f, b, a);
    }
  };
}

static <A> Comparator<A> makeReversedComparator(Comparator<A> c) {
  ret (a, b) -> c.compare(b, a);
}