static <A> L<A> prioritizeList(Collection<A> c, L<A> prioritizer) {
  new L<A> l;
  Set<A> set = asSet(c);
  for (A a : prioritizer) {
    if (set.contains(a)) {
      set.remove(a);
      l.add(a);
    }
  }
  l.addAll(set);
  ret l;
}