(define (list-of-squares nums)
  (define (square (car nums))
    (* (car nums) (car nums)))
  (if (null? nums)
      nil
      (cons (square (car nums))
	    (list-of-squares (cdr nums)))))




(set! (cdr x) nil)





(define (assq sym alis)
  (cond ((null? alis) nil)
	((eq? sym (caar alis))
	 (car alis))
	(else
	 (set! alis (cdr alis))
	 (assq sym alis))))