sicp exercise 2.7

; Exercise 2.7.  Alyssa's program is incomplete because she has not specified the implementation of the interval abstraction. Here is a definition of the interval constructor:

;(define (make-interval a b) (cons a b))

;Define selectors upper-bound and lower-bound to complete the implementation.



(define (make-interval a b) (cons a b))
(define (upper-bound interval) (car interval))
(define (lower-bound interval) (cdr interval))