SICP 問題2.25
(1 3 (5 7) 9) (car (cdr (car (cdr (cdr))))) ((7)) (car (car )) (1 (2 (3 (4 (5 (6 7)))))) (car (cdr (car (cdr (car (cdr (car (cdr (car (cdr (car (cdr ))))))))))))
gosh> (car (cdr (car (cdr (cdr '(1 3 (5 7) 9)))))) 7 gosh> (car (car '((7)))) 7 gosh> (car (cdr (car (cdr (car (cdr (car (cdr (car (cdr (car (cdr '(1 (2 (3 (4 (5 (6 7)))))))))))))))))) 7