Exercise 4.37.  Ben Bitdiddle claims that the following method for 
generating Pythagorean triples is more efficient than the one in 
exercise 4.35. Is he correct? (Hint: Consider the number of 
possibilities that must be explored.)

(define (a-pythagorean-triple-between low high)
  (let ((i (an-integer-between low high))
        (hsq (* high high)))
    (let ((j (an-integer-between i high)))
      (let ((ksq (+ (* i i) (* j j))))
        (require (>= hsq ksq))
        (let ((k (sqrt ksq)))
          (require (integer? k))
          (list i j k))))))

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He is correct.  For many values of j, the entire branch will be 
eliminated from consideration at the (require (>= hsq ksq)) step.  
Instead of testing all possible values of k, only one test is performed 
per i,j pair.