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