# SICP - Solution: Exercise 2.7

##### January 9, 2019

## 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.

## Solution #

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