(define s (cons-stream 1 (cons-stream 2 nil)))

(define (constant-stream i)
  (cons-stream i (constant-stream i))
)

(define (nats start)
  (cons-stream start (nats (+ start 1)))
)

(define (add-stream s1 s2)
  (cons-stream (+ (car s1) (car s2))
               (add-stream (cdr-stream s1) (cdr-stream s2)))
)

(define ones (cons-stream 1 ones))
(define ints (cons-stream 1 (add-stream ones ints)))

(define (prefix s k)
  (if (= k 0)
      nil
      (cons (car s) (prefix (cdr-stream s) (- k 1)))
  )
)

(define (map-stream f s)
  (if (null? s)
      nil
      (cons-stream (f (car s)) (map-stream f (cdr-stream)))
  )
)