(define (average x y) (/ (+ x y) 2))
(define (make-segment s e) (cons s e))
(define (start-segment seg) (car seg))
(define (end-segment seg) (cdr seg))
(define (make-point x y) (cons x y))
(define (x-point p) (car p))
(define (y-point p) (cdr p))
(define (midpoint-segment seg)
(make-point
(average (car (car seg)) (car (cdr seg)))
(average (cdr (car seg)) (cdr (cdr seg)))))
(define (print-point p)
(display "(")
(display (x-point p))
(display ",")
(display (y-point p))
(display ")")
(newline))
(define p1 (make-point 0 0))
(define p2 (make-point 2 2))
(define seg (make-segment p1 p2))
(print-point (midpoint-segment seg))
