Exercise 2.25 · 习题

Exercise 2.25: Give combinations of cars
and cdrs that will pick 7 from each of the following lists:

(1 3 (5 7) 9)

((7))

(1 (2 (3 (4 (5 (6 7))))))

练习 2.25：给出能从下列各表中取出 7 的 car 与 cdr 的组合式：

(1 3 (5 7) 9)
((7))
(1 (2 (3 (4 (5 (6 7))))))