anchor.diff:  import "dart:collection";
  +import "dart:async";
   import "Command.dart";
   import "Block.dart";
   import "dart:math";
   import "Level.dart";
   import "Cursor.dart";
   
  +enum eventType
  +{
  +  Win,
  +  GameOver
  +}
  +
  +
   class Playfield
   {
  +  static int unusableRows = 1;
     List<List<Block>> _field;
     Queue<Command> _actionQueue = new Queue<Command>();
  -  //Streamcontroller hier kommt der eventhandler hin
  +  StreamController _eventController = new StreamController.broadcast();
  +
     double _currentScore;
  -  int _currentLevelTime;
  +  int _currentLevelTime; // in seconds
     List<Block> _toDissolve;
     int _fieldX;
     int _fieldY;
  
positive.code:         for(int y = currentBlockPos.y; y < _fieldY; y++)
          {
            _field[currentBlockPos.x][y].setFalling(true);
          }
  
          // add Points to Score
  
negative.code:   {
      bool valid = false;
  
      ((coordinate.x >= 0 + unusableRows) && (coordinate.x < _fieldX)) ? valid = true : valid = false;
      ((coordinate.y >= 0 + unusableRows) && (coordinate.y < _fieldY)) ? valid = true : valid = false;
  
      throw new Exception("not tested yet");
  
      return valid;
    }
  
  
    /**
  