\begin{algorithm}
        \caption{Union of Circular, Doubly Linked List}
        \begin{algorithmic}
        \INPUT Circular, doubly linked list with a sentinel $L_1$ and $L_2$
        \OUTPUT $L_1 \cup L_2$
            \STATE $L_2.nil.next.prev = L_1.nil.prev$
            \STATE $L_1.nil.prev.next = L_2.nil.next$
            \STATE $L_2.nil.prev.next = L_1.nil$
            \STATE $L_1.nil.prev = L_2.nil.prev$
            \RETURN $L_1$
        \end{algorithmic}
        \end{algorithm}