Exercise 4.70: What is the purpose of the
let bindings in the procedures add-assertion! and
add-rule!?  What would be wrong with the following implementation of
add-assertion!?  Hint: Recall the definition of the infinite stream of
ones in 3.5.2: (define ones (cons-stream 1 ones)).


(define (add-assertion! assertion)
  (store-assertion-in-index assertion)
  (set! THE-ASSERTIONS
        (cons-stream assertion 
                     THE-ASSERTIONS))
  'ok)