anchor.diff:    final Field field;
     final Array2d<SquareState> _states;
     final EventHandle<EventArgs> _updatedEvent;
  +  final EventHandle<GameState> _gameStateEvent;
   
     GameState _state;
     int _minesLeft;
  
positive.code:   GameState get state() => _state;
  
    EventRoot get updated() => _updatedEvent;
  
    SquareState getSquareState(int x, int y) => _states.get(x,y);
  
  
negative.code:   void _update() => _updatedEvent.fireEvent(EventArgs.empty);
  
    void _setState(GameState value) {
      assert(value != null);
      assert(_state != null);
      assert((_state == GameState.reset) == (_startTime == null));
      if(_state != value) {
        _state = value;
  