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

(define (square-tree tree)
  (cond ((null? tree) '())
	((not (pair? tree)) (square tree))
	(else
	  (cons (square-tree (car tree)) 
		(square-tree (cdr tree))))))

(define (square-tree-map tree)
  (map (lambda (sub-tree)
	 (if (pair? sub-tree)
	     (square-tree-map sub-tree)
	     (square sub-tree)))
       tree))

(define (tree-map fn tree)
  (map (lambda (sub-tree)
	 (if (pair? sub-tree)
	     (tree-map fn sub-tree)
	     (fn sub-tree)))
       tree))