anchor.diff:      }
       return newNode;
     }
  -}
  -
  -_updateVNode(_VNode node, Owner ownerID, int level, int index, value, Bool didAlter) {
  -  if (node == null) {
  -    var t = new _VNode([], new Owner());
  -    return t._update(ownerID, level, index, value, didAlter);
  -  }
  -  return node._update(ownerID, level, index, value, didAlter);
   }
   
   _VNode _transientVNode(_VNode node, Owner ownerID) {
  
positive.code:   }
  
    TransientVectorImpl _clear() {
      this._size = 0;F_
      this._level = _SHIFT;
      this._root = this._tail = null;
      this._hashCode = null;
  
negative.code:       } else {
          lowerNode = null;
        }
        var newLowerNode = lowerNode._update(ownerID, level - _SHIFT, index, value, didAlter);
        if (newLowerNode == lowerNode) {
          return node;
        }
  