; Aufgabe 2a
(define (list-ref list index)
  (define (l-r-itter list index)
    (cond ((< 0 index) (l-r-itter (cdr list) (- index 1)))
          (else (car list))))
  (l-r-itter list index))

; Aufgabe 3b
(require (lib "graphics.ss" "graphics"))
(open-graphics)
(require (lib "trace"))
(define (draw-polygon viewport polygon)
  (cond ((not(null? polygon)) ((draw-line viewport) (list-ref polygon 0) (list-ref polygon 1)) (draw-polygon viewport (cdr polygon)))
        (else (display "done") (newline))))
(trace draw-polygon)
(draw-polygon (open-viewport "Ein großes N" 100 100) 
              (list (make-posn 20 80) (make-posn 20 20) 
                    (make-posn 80 80) (make-posn 80 20)))