anchor.diff:  }
   
   class Game {
  -  static const int GAME_SPEED = 50;     // smaller numbers are faster
  +  // smaller numbers make the game run faster
  +  static const num GAME_SPEED = 50;
   
  -  Random _random;
  -  num _lastTimestamp = 0;
  +  num _lastTimeStamp = 0;
  +
  +  // a few convenience variables to simplify calculations
     int _rightEdgeX;
     int _bottomEdgeY;
   
  
positive.code:   }
  
    void init() {
      _random = new Random();
      _snake = new Snake();
      _food = _randomPoint();
    }
  
    Point _randomPoint() {
      return new Point(_random.nextInt(_rightEdgeX), _random.nextInt(_bottomEdgeY));
    }
  
    void _checkForCollisions() {
      // check death conditions
      if (_snake.head.x <= -1 || _snake.head.x >= _rightEdgeX ||
        _snake.head.y <= -1 || _snake.head.y >= _bottomEdgeY ||
        _snake.checkForBodyCollision()) {
        init();
        return;
      }
  
      // check for collision with food
      if (_snake.head == _food) {
        _food = _randomPoint();
        _snake.grow();
      }
    }
  
  
negative.code:   }
  
    void update(num delta) {
      final num diff = delta - _lastTimeStamp;
  
      if (diff > GAME_SPEED) {
        _lastTimeStamp = delta;
        clear();
        drawCell(_food, "blue");
        _snake.update();
  