問題2.52

(add-load-path ".")
(load "2.49.scm")

(define (corner-split2 painter n)
  (if (= n 0)
      painter
      (let ((right (right-split painter (- n 1)))
            ((up (rotate90 (right-split (rotate270 painter))))))
        (let ((top-left (beside up up))
              (bottom-right (below right right))
              (corner (corner-split painter (- n 1))))
          (beside (below painter top-left)
                  (below bottom-right corner))))))