scheme@(guile-user)> (define output (Heaps-stream (list->stream input)))
scheme@(guile-user)> (stream-for-each (lambda (s) (display (stream->list s)) (newline)) (stream-take (* 1 2 3 4 5 6 7) output))
(a b c d e f g)
(b a c d e f g)
(c a b d e f g)
(a c b d e f g)
(b c a d e f g)
(c b a d e f g)
(d b a c e f g)
(b d a c e f g)
(a d b c e f g)
(d a b c e f g)
(b a d c e f g)
(a b d c e f g)
(a c d b e f g)
(c a d b e f g)
(d a c b e f g)
(a d c b e f g)
(c d a b e f g)
(d c a b e f g)

...

(c g b d e f a)
(b g c d e f a)
(g b c d e f a)
scheme@(guile-user)> (define n (stream-from 0)) ; a stream of natural numbers from 0
scheme@(guile-user)> (define s (Heaps-stream n))
scheme@(guile-user)> (stream->list (stream-take 10 (stream-ref s 0)))
$1 = (0 1 2 3 4 5 6 7 8 9)
scheme@(guile-user)> (stream->list (stream-take 10 (stream-ref s 1)))
$2 = (1 0 2 3 4 5 6 7 8 9)
scheme@(guile-user)> (stream->list (stream-take 10 (stream-ref s 2)))
$3 = (2 0 1 3 4 5 6 7 8 9)
scheme@(guile-user)> (stream->list (stream-take 10 (stream-ref s 100)))
$4 = (4 1 3 2 0 5 6 7 8 9)
scheme@(guile-user)> (stream->list (stream-take 10 (stream-ref s 1000)))
$5 = (2 6 0 1 5 4 3 7 8 9)
scheme@(guile-user)> (stream->list (stream-take 10 (stream-ref s 10000)))
$6 = (3 4 0 2 1 5 7 6 8 9)
scheme@(guile-user)> (stream->list (stream-take 10 (stream-ref s 100000)))
$7 = (5 0 8 1 7 2 3 6 4 9)
scheme@(guile-user)>