public void remove (DNode v)
 {
     DNode oldPrevious = v.previous;
     DNode oldNext = v.next;
     oldPrevious.next = oldNext;
     oldNext.previous = oldPrevious;
          
 }
        public DoubleStringLinkedList()
        {
            m_head = new DNode(); 
            m_tail = new DNode();

            m_head.next = m_tail;
            m_tail.previous = m_head;
        }
        public DNode addBefore(DNode v , string newItem )
        {
            DNode u =new DNode();
            u.element = newItem;
            DNode oldPrevious = v.previous;
            
            u.next = v;
            u.previous = oldPrevious;

            v.previous = u;
            oldPrevious.next = u;

            return u;
        }