問題2-48 (2.2.4 Example: A Picture Language)

webにおけるSICP（笑）への流れが。。流れが。。

(define (make-segment start-point end-point)
  (cons start-point end-point))
(define (start-segment segment)
  (car segment))
(define (end-segment segment)
  (cadr segment))