# Interval Subtraction

From the Extended Exercise beginning in section 2.1.4, you can find exercise 2.8:

Exercise 2.8. Using reasoning analogous to Alyssa's, describe how the difference of two intervals may be computed. Define a corresponding subtraction procedure, called sub-interval.

I wrote the following:

(define (sub-interval x y)
(make-interval (- (lower-bound x) (upper-bound y))
(- (upper-bound x) (lower-bound y))))


What do you think?

Looks great. Don't forget to define lower-bound and upper-bound as car and cdr respectively.