Exercise 4.74.  Alyssa P. Hacker proposes to use a simpler version of 
stream-flatmap in negate, lisp-value, and find-assertions. She observes 
that the procedure that is mapped over the frame stream in these cases 
always produces either the empty stream or a singleton stream, so no 
interleaving is needed when combining these streams.

a. Fill in the missing expressions in Alyssa's program.

(define (simple-stream-flatmap proc s)
  (simple-flatten (stream-map proc s)))

(define (simple-flatten stream)
  (stream-map <??>
              (stream-filter <??> stream)))

b. Does the query system's behavior change if we change it in this way?

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a.

(define (simple-stream-flatmap proc s)
  (simple-flatten (stream-map proc s)))

(define (simple-flatten stream)
  (stream-map stream-car
              (stream-filter (lambda (x) (not (stream-null? x))) stream)))

b.

It seems that this is equivalent to the more complex stream-flatten in 
how and when it calls the procedure and returns the results, so I think 
the behavior will be the same.