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