(define (cycles-1? r)
  (define checklist '())
  (define (loop r)
    (cond ((null? r) #f)
          ((memq r checklist) #t)
          (else
            (set! checklist (cons r checklist))
            (loop (cdr r)))))
  (loop r))
(define (cycles-2? r)
  (define (check-until-pos lst pos wat)
    (if (= pos 0)
        #f
        (if (eq? lst wat)
            #t
            (check-until-pos (cdr lst) (-1+ pos) wat))))
  (define (looplst lst aantal)
    (cond ((null? lst) #f)
          ((check-until-pos r aantal lst) #t)
          (else (looplst (cdr lst) (1+ aantal)))))
  (looplst r 0))