Exercise 2.24.  Suppose we evaluate the expression (list 1 (list 2 (list 
3 4))). Give the result printed by the interpreter, the corresponding 
box-and-pointer structure, and the interpretation of this as a tree (as 
in figure 2.6).

————————————————————————————————————————————————————————————————————————

(1 (2 (3 4)))

┌───┬───┐   ┌───┬───┐
│ · │ · ├─▶ │ · │ / │
└─┬─┴───┘   └─┬─┴───┘
  ▼           ▼
  1         ┌───┬───┐   ┌───┬───┐
            │ · │ · ├─▶ │ · │ / │
            └─┬─┴───┘   └─┬─┴───┘
              ▼           ▼
              2         ┌───┬───┐   ┌───┬───┐
                        │ · │ · ├─▶ │ · │ / │
                        └─┬─┴───┘   └─┬─┴───┘
                          ▼           ▼
                          3           4

The following expression is equivalent:

(cons 1 (cons (cons 2 (cons (cons 3 (cons 4 '())) '())) '()))

As a tree:

       .
      / \
     1  /\
       2  \
          /\
         3  4