#lang planet neil/sicp

	(define (check-loop x)
	  (let ((checked-list '()))
	    (define (check-loop-temp x)
	      (cond ((null? x) false)
	            ((checked? (car x)) true)
	            (else
	             (begin (set! checked-list (cons (car x) checked-list))
	                    (check-loop-temp (cdr x))))))

	    (define (checked? x)
	      (define (checked-temp? x checked-list)
	        (cond ((null? checked-list) false)
	              ((eq? (car checked-list) x) true)
	              (else (checked-temp? x (cdr checked-list)))))
	      (checked-temp? x checked-list))

	    (check-loop-temp x)))

	(define z (cons 'a (cons 'b (cons 'c '()))))
	(set-cdr! (cddr z) z)

	(check-loop z)