virtual void* operator()(void* anItem) { void* result=mOtherTree.FindItem(anItem);
virtual const void* operator()(const void* anItem) { const void* result=mOtherTree.FindItem(anItem);
  virtual void* operator()(void* anItem) {    void* result=mOtherTree.FindItem(anItem);    if(result)      return nsnull;    return anItem;  }