sol-2.25.tex

If we let $x$, $y$, $z$ be the three lists
\begtt\scm
(define x (list 1 3 (list 5 7) 9))
(define y (list (list 7)))
(define z (list 1 (list 2 (list 3 (list 4 (list 5 (list 6 7)))))))
\endtt
then we can pick $7$ from each of them in the following ways:
\begtt\scm
(car (cdr (car (cdr (cdr x)))))
;Value: 7
(car (car y))
;Value: 7
(car (cdr (car (cdr (car (cdr (car (cdr (car (cdr (car (cdr z))))))))))))
;Value: 7
\endtt