Exercise 3.51.  In order to take a closer look at delayed evaluation, we 
will use the following procedure, which simply returns its argument 
after printing it:

(define (show x)
  (display-line x)
  x)

What does the interpreter print in response to evaluating each 
expression in the following sequence?

(define x (stream-map show (stream-enumerate-interval 0 10)))
(stream-ref x 5)
(stream-ref x 7)

————————————————————————————————————————————————————————————————————————

> (define x ...)
0
x
> (stream-ref x 5)
1
2
3
4
5
5
> (stream-ref x 7)
6
7
7