anchor.diff:  
     onKeyDown(KeyboardEvent event) {
       event.preventDefault();
  -    print("Key event");
       Coord d = getDirectionFromKeyboardEvent(event);
       if (d != null && tailTurnFilter(d, direction)) {
         direction = d;
  
positive.code: 
      final Coord newHead = headCoord.copy();
      assert(newHead != null);
      print("length = ${coords.length}");
      newHead.add(direction);
  
      print("head.x = ${newHead.x} head.y=${newHead.y}");
      if (!isOnCanvas(newHead)) {
        collisionWithCanvas();
        return;
  
negative.code:     points += delta;
    }
  
  
  
    void showPoints() {
      var pts = querySelector("#points");
  