anchor.diff:    BaseVectorImpl _withMutations(fn) {
       var mutable = this._asMutable();
       fn(mutable);
  -    return mutable.wasAltered() ? mutable._ensureOwner(this.__ownerID) : this;
  +    return mutable.wasAltered() ? mutable._ensureOwner(this._owner) : this;
     }
   
   }
  
positive.code:       newTail = newTail._removeAfter(owner, 0, newSize);
      }
  
      if (__ownerID != null) {
        _size = newSize;
        _origin = 0;
        _level = newLevel;
  
negative.code:     var newRoot = vector._root;
      var didAlter = new Bool();
      if (index >= _getTailOffset(vector._size)) {
        newTail = _updateVNode(newTail, vector._owner, 0, index, value, didAlter);
      } else {
        newRoot = _updateVNode(newRoot, vector._owner, vector._level, index, value, didAlter);
      }
      if (!didAlter.value) {
        return vector;
      }
      if (vector._owner != null) {
        vector._root = newRoot;
        vector._tail = newTail;
        vector.__altered = true;
  