public  Object previousElement() { return vertices.elementAt(tail_--); }
    public /*synchronized*/ boolean hasMoreElements() {	return enum.hasMoreElements();    }    /** previousElement() - returns elements starting at the end of        the vector and working to the front. Behavior is undefined if        you add to or remove elements from the Vector while you're        iterating. does not wrap the index. */    public /*synchronized*/ Object previousElement()    {	return vertices.elementAt(tail_--);    }