anchor.diff:  
       // Set game over
       _isGameOver = true;
  +    _gameOverFrame = _numFrames;
       _gameOverCallback(_hud.score);
   
       // Remove the ship
  
positive.code: 
      // Add an explosion
      addExplosion(AsteroidSize.large, _ship.position);
  
      _navigator.pop();
    }
  
    // Handling controls
  
negative.code:   // Game state
    int _numFrames = 0;
    bool _isGameOver = false;
    int _gameOverFrame;
    int _currentLevel = 0;
  
    // Heads up display
  