abstract sclass NotifyingMap<A, B> extends AbstractMap<A, B> {
  Map<A, B> map; // backing map

  *() {} // for persistence
  *(Map<A, B> *map) {}
  
  get() {
  }

  abstract void change();
  
  Map<A, B> unwrap() { ret map; }
}

Began life as a copy of #1013865