static <A, B> Map<A, B> minimalNotifyingMap(Map<A, B> map, Runnable notify) {
  ret new AbstractMap<A, B>() {
    public Set<Map.Entry<A, B>> entrySet() { throw unimplemented(); }
    
    public B put(A a, B b) {
      B result = map.put(a, b);
      pcallF(notify);
      ret result;
    }
  };
}