anchor.diff:  }
   
   init() {
  -  entities.add(new Ship(100, 100));
  +  entities.add(new Ship(100, 250));
   
  -  int invaderStartX = 20;
  +  int invaderStartX = sceneLeft + 10;
     int invaderStartY = 40;
     int invaderGapX = 30;
     int invaderGapY = 35;
  
positive.code:   InvaderController(this._invaders);
  
    int _updateIdx = 0;
  
    update(UpdateContext u) {
      int row = _updateIdx % numRows;
      int firstInvader = row * numCols;
      int lastInvader = firstInvader + numCols;
      for (int i = firstInvader; i < lastInvader; i++) {
        _invaders[i].x += 1;
      }
  
      _updateIdx++;
    }
  
negative.code: library pewpewgame;
  
  import 'dart:html';
  import 'dart:math';
  import 'package:game_loop/game_loop_html.dart';
  import 'package:pewpew/gamewrapper.dart';
  
  
  const int sceneLeft = 10;
  const int sceneRight = 500;
  
  const int numRows = 5;
  const int numCols = 11;
  
  
  List<Invader> invaders = new List<Invader>();
  
  