From d7bcd52fd0910d8bc9d16798aafb2391b130648f Mon Sep 17 00:00:00 2001
From: Tobias Eidelpes <tobias@eidelpes.info>
Date: Sat, 5 Nov 2022 12:50:28 +0100
Subject: [PATCH] Add exercise 2.8

---
 chapter2.lisp | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/chapter2.lisp b/chapter2.lisp
index 1c8cce4..6a76738 100644
--- a/chapter2.lisp
+++ b/chapter2.lisp
@@ -85,3 +85,8 @@
    (make-interval (/ 1.0 (upper-bound b))
 		  (/ 1.0 (lower-bound b)))))
 
+;; Exercise 2.8
+(defun sub-interval (a b)
+  (make-interval (- (lower-bound b) (lower-bound a))
+		 (- (upper-bound b) (upper-bound a))))
+