HHGBOT-2> (defun forward (cursor)
             (cons (list* (cadr cursor) (car cursor))
                   (cdr (cdr cursor))))
 FORWARD
 HHGBOT-2> (defun backward (cursor)
             (cons (cdr (car cursor))
                   (list* (car (car cursor)) (cdr cursor))))
 BACKWARD
 HHGBOT-2> (forward '(nil . (1 2 3)))
 ((1) 2 3)
 HHGBOT-2> (forward *)
 ((2 1) 3)
 HHGBOT-2> (forward *)
 ((3 2 1))
 HHGBOT-2> (backward *)
 ((2 1) 3)
 HHGBOT-2> (backward *)
 ((1) 2 3)
 HHGBOT-2> (backward *)
 (NIL 1 2 3)