(define (iterate start-value next-value start-index next-index finished?)
  (define (inner-iter cur-val cur-index)
    (if (finished? cur-val cur-index)
        cur-val
        (inner-iter (next-value cur-val cur-index) (next-index cur-val cur-index))))
  (inner-iter start-value start-index))

; b)
(define (phi n)
  (if (= n 0)
      1.0
      (iterate
       1.0 (lambda (cur-val cur-index) (+ 1 (/ 1 cur-val)))    ; Start-Wert und Werteberechnung (1+1/vorherigen wert)
       0 (lambda (cur-val cur-index) (+ cur-index 1))          ; Start-Index und Indexerhöhung (index++)
       (lambda (cur-val cur-index) (if (= n cur-index) #t #f)) ; Endabfrage (index == n)
       )))