anchor.diff:  }
   
   class FallingPieces extends Pieces { 
  +  
     FallingPieces(int count) {
       createFallingPieces(count);
     }
  
positive.code: }
  
  class MovablePieces extends Pieces { 
    MovablePieces(int count) {
      createMovablePieces(count);
    }
  
negative.code:   randomInit() => forEach((MovablePiece mp) => mp.randomInit()); 
    onOff() => forEach((MovablePiece mp) => mp.onOff());
    
    bool avoidCollisions(MovablePiece mp) {
      bool isCollisionAvoided = false;
      for (var p in this) {
        if (p != mp) {
  