static <A, B> L<Pair<A, B>> pairsSortedByADesc(Collection<Pair<A, B>> l) {
  ret sortedByComparator(l, new Comparator<Pair<A, B>>() {
    public int compare(Pair<A, B> a, Pair<A, B> b) {
      ret cmp(b.a, a.a);
    }
  });
}

Began life as a copy of #1025274