SICP Exercise 2.30 square-tree

Exercise 2.30.  Define a procedure square-tree analogous to the square-list procedure of exercise 2.21. That is, square-list should behave as follows:


(square-tree
 (list 1
       (list 2 (list 3 4) 5)
       (list 6 7)))
(1 (4 (9 16) 25) (36 49))


Define square-tree both directly (i.e., without using any higher-order procedures) and also by using map and recursion.

SOLUTION
The code and tests are here.

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