2.1|

$ cd ~

SICP Exercise 2.10

Interval spanning zero means one end is less than 0 and the other is greater than 0.

(define (div-interval x y)
(if (and (<= (lower-bound y) 0) (>= (upper-bound y) 0))
    (error "Interval spans 0")
    (mul-interval x
                  (make-interval (/ 1.0 (upper-bound y))
                                 (/ 1.0 (lower-bound y))))))