Exercise 2.45.  Right-split and up-split can be expressed as instances 
of a general splitting operation. Define a procedure split with the 
property that evaluating

(define right-split (split beside below))
(define up-split (split below beside))

produces procedures right-split and up-split with the same behaviors as 
the ones already defined.

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(define (split primary secondary)
  (define (go painter n)
    (if (= n 0)
        painter
        (let ((smaller (go painter (- n 1))))
          (primary painter (secondary smaller smaller)))))
  go)