anchor.diff:        //    'COLOR: ${this._game.field[cell['row']][cell['col']].color}');
         if(this._game.field[cell['row']][cell['col']].color != #empty &&
             !this._game.field[cell['row']][cell['col']].isActive){
  -        return true;
  +          return true;
         }
       }
   
  
positive.code:           this._stone.forEach((piece) {
              this._game._field[piece['row']][piece['col']].isActive = true;
            });
          } else{
            //den Tetromino bei einer Kollision an der Position setzen
            this._stone.forEach((piece) {
              this._game._field[piece['row']][piece['col']].isActive = false;
            });
            //TODO: check if a row was completed
            nextTetromino();
          }
        } else {
          this._stone.forEach((piece) {
  
negative.code:       if (notOnGround(move)){
          //pruefen ob der Tetromino mit einem bereits gesetzten Tetromino kollidiert
          if(!tetrominoCollision(move)) {
            //den Tetromino in der alten Position entfernen
            this._stone.forEach((piece) {
              this._game._field[piece['row']][piece['col']].isActive = false;
              this._game._field[piece['row']][piece['col']].color = #empty;
  