Exercise 4.71: Louis Reasoner wonders why the
simple-query and disjoin procedures (4.4.4.2) are
implemented using explicit delay operations, rather than being defined
as follows:


(define (simple-query 
         query-pattern frame-stream)
  (stream-flatmap
   (lambda (frame)
     (stream-append
      (find-assertions query-pattern frame)
      (apply-rules query-pattern frame)))
   frame-stream))

(define (disjoin disjuncts frame-stream)
  (if (empty-disjunction? disjuncts)
      the-empty-stream
      (interleave
       (qeval (first-disjunct disjuncts)
              frame-stream)
       (disjoin (rest-disjuncts disjuncts)
                frame-stream))))

Can you give examples of queries where these simpler definitions would lead to
undesirable behavior?