anchor.diff:  
     _get(int index) => (index >= 0 && index < this.length) ? this._array[index] : null;
   
  -  VNode _removeAfter(Owner ownerID, int level, int index) {
  +  _VNode _removeAfter(Owner ownerID, int level, int index) {
       if ((index == (level > 0 ? 1 << level : 0 ))|| this.length == 0) {
         return this;
       }
  
positive.code: 
  }
  
  class VNode {
    List _array;
    Owner _ownerID;
  
  
negative.code:   BaseVectorImpl._prototype() {
      this._origin = 0;
      this.__ownerID = null;
      this._root = new _VNode([], __ownerID);
      this._tail = _root;
      this._level = _SHIFT;
      this._size = 0;
  