Exercise 5.1.  Design a register machine to compute factorials using the 
iterative algorithm specified by the following procedure. Draw data-path 
and controller diagrams for this machine.

(define (factorial n)
  (define (iter product counter)
    (if (> counter n)
        product
        (iter (* counter product)
              (+ counter 1))))
  (iter 1 1))

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see 5.1.svg