anchor.diff:    // Game state
     int _numFrames = 0;
     bool _isGameOver = false;
  +  int _currentLevel = 0;
   
     // Heads up display
     Hud _hud;
  
positive.code: 
      _gameLayer = new Node();
      this.addChild(_gameLayer);
  
      // Add some asteroids to the game world
      for (int i = 0; i < 5; i++) {
        addAsteroid(AsteroidSize.large);
      }
      for (int i = 0; i < 5; i++) {
        addAsteroid(AsteroidSize.medium);
      }
  
      // Add ship
      addShip();
  
  
negative.code:     }
      return true;
    }
  
    // Scoring and HUD
    void addScore(int score) {
      _hud.score += score;
    }
  }
  
  // Game objects
  