anchor.diff:  
     create() {
   
  -    game.world.setBounds(0, 0, 250, 250);
  +    //game.world.setBounds(0, 0, 250, 250);
   
       game.physics.startSystem(Physics.ARCADE);
   
  
positive.code: 
      cursors = game.input.keyboard.createCursorKeys();
  
      game.camera.follow(ship);
    }
  
    update() {
  
negative.code:     aliens = game.add.group();
      aliens.enableBody = true;
  
      for (var i = 0; i < 200; i++) {
        Sprite s = aliens.create(game.world.randomX, game.world.randomY, 'baddie');
        s.scale.set(1);
        s.body.collideWorldBounds = true;
  