(define l1 (list-n 500))

(define access-list
  (lambda (l n)
    (if (zero? n) l
        (access-list (cdr l) (- n 1)))))
(set-cdr! (access-list l1 250) '())

(define l2 (list-n 500))

;; (list-n 100)

(list-n 1000)

;; (list-n 200)