#lang sicp

(define (square x) (* x x))

;(define (square-tree tree)
;  (cond ((null? tree) '())
;        ((number? tree) (square tree))
;        (else (cons (square-tree (car tree))
;                    (square-tree (cdr tree))))))
(define (square-tree tree)
  (if (number? tree)
      (square tree)
      (map square-tree tree)))