#| BEGIN (Write your solution here) |#
(define (triples s t u)
  (cons-stream
   (list (stream-car s)
         (stream-car t)
         (stream-car u))
   (interleave
    (stream-map
     (lambda (x) (cons (stream-car s) x))
     (pairs t (stream-cdr u)))
    (triples (stream-cdr s) (stream-cdr t) (stream-cdr u)))))

(define pythagorean-triples
  (stream-filter
   (lambda (triple) (= (+ (square (car triple))
                          (square (cadr triple)))
                       (square (caddr triple))))
   (triples integers integers integers)))
#| END |#