anchor.diff:        _states[i] = SquareState.hidden;
         _minesLeft++;
       }
  +    _update();
     }
   
     void reveal(int x, int y) {
  
positive.code:   int get revealsLeft => _revealsLeft;
  
    GameState get state => _state;
  
    SquareState getSquareState(int x, int y) {
      final i = field._getIndex(x, y);
  
negative.code: class Game {
    final Field field;
    final List<SquareState> _states;
    final EventHandle<EventArgs> _updatedEvent;
  
    GameState _state;
    int _minesLeft;
  