A simpler version of stream-flatmap

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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