(define pi1-stream
  (lambda (S)
    (letrec ((helper
              (lambda (l)
                (if (stream-empty? l)
                    empty-stream
                    (stream-cons (stream-first l)
                                 (helper (stream-filter
                                          (lambda (x) (not (equal? x (stream-first l))))
                                          (stream-rest l))))))))
      (helper (stream-map (lambda (x) (stream-first x)) S)))))

(define pi2-stream
  (lambda (S)
    (letrec ((helper
              (lambda (l)
                (if (stream-empty? l)
                    empty-stream
                    (stream-cons (stream-first l)
                                 (helper (stream-filter
                                          (lambda (x) (not (equal? x (stream-first l))))
                                          (stream-rest l))))))))
      (helper (stream-map (lambda (x) (stream-first (stream-rest x))) S)))))

(stream->listn (pi1-stream (cart-streams integers integers)) 10)
(stream->listn (pi2-stream (cart-streams integers integers)) 10)