1 665c255d 2023-08-04 jrmu (define (cycle? x)
 2 665c255d 2023-08-04 jrmu   (let ((aux '()))
 3 665c255d 2023-08-04 jrmu     (define (find-cycle z)
 4 665c255d 2023-08-04 jrmu       (cond ((null? z) false)
 5 665c255d 2023-08-04 jrmu 	    ((memq z aux) true)
 6 665c255d 2023-08-04 jrmu 	    (else 
 7 665c255d 2023-08-04 jrmu 	     (set-cdr! (last-pair aux) (list z))
 8 665c255d 2023-08-04 jrmu 	     (find-cycle (cdr z)))))
 9 665c255d 2023-08-04 jrmu     (if (not (pair? x))
10 665c255d 2023-08-04 jrmu 	(error "argument of cycle? must be a pair."))
11 665c255d 2023-08-04 jrmu     (set! aux (list x))
12 665c255d 2023-08-04 jrmu     (find-cycle (cdr x))))