;; The first three lines of this file were inserted by DrScheme. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "reader.ss" "plai" "lang")
;; DATA DEFINITION
;; A point has 
;;   an x isa number
;;   a  y isa number
(define-struct point (x y))

;; CONTRACT
;; make-point :: number number -> point

;; CONTRACT
;; point-x :: point -> number

;; CONTRACT
;; point? :: any -> boolean