anchor.diff:      if (pos != null) asteroid.position = pos;
       _gameLayer.addChild(asteroid);
       _asteroids.add(asteroid);
  +
  +    // Animate asteroid into the scene
  +    Action action = new ActionTween((a) => asteroid.scale = a, 0.0, 1.0, 1.0, bounceOut);
  +    _gameLayer.actions.run(action);
     }
   
     void addShip() {
  
positive.code:   SpriteSheet spriteSheetUI;
    Sprite sprtBgScore;
    Sprite sprtBgShield;
  
    int _score = 0;
  
  
negative.code:     }
      return true;
    }
  
    // Scoring and HUD
    void addScore(int score) {
      _hud.score += score;
    }
  }
  
  // Game objects
  