(define (stream-section n stream)
  (cond ((= n 0) '())
        (else 
          (cons 
            (head stream)
            (stream-section 
             (- n 1)
             (tail stream))))))

(define (add-streams s1 s2)
 (let ((h1 (head s1))
       (h2 (head s2)))
   (cons-stream 
     (+ h1 h2)
     (add-streams (tail s1) (tail s2)))))