SICP問題2.25

(1 3 (5 7) 9)から7を取り出すcarとcdrの組み合わせ

(list 1 3 (list 5 7) 9)
(car (cdr (car (cdr (cdr (list 1 3 (list 5 7) 9))))))
; 7

((7))から7を取り出すcarとcdrの組み合わせ

(list (list 7))
(car (car (list (list 7))))
; 7

(1 (2 (3 (4 (5 (6 7))))))から7を取り出すcarとcdrの組み合わせ

(list 1 (list 2 (list 3 (list 4 (list 5 (list 6 7))))))
(car (cdr (car (cdr (car (cdr (car (cdr (car (cdr (car (cdr (list 1 (list 2 (list 3 (list 4 (list 5 (list 6 7))))))))))))))))))
; 7