```
(define (make-point x y) (cons x y))
(define (x-point p) (car p))
(define (y-point p) (cdr p))
(define (print-point p)
(newline)
(display "(")
(display (x-point p))
(display ",")
(display (y-point p))
(display ")"))
(define (make-segment start-point end-point)
(cons start-point end-point))
(define (start-segment segment) (car segment))
(define (end-segment segment) (cdr segment))
(define (midpoint-segment segment)
(define (average a b) (/ (+ a b) 2))
(let ((a (start-segment segment))
(b (end-segment segment)))
(make-point (average (x-point a)
(x-point b))
(average (y-point a)
(y-point b)))))
```