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diff --git a/net/ricketyspace/sicp/two/seven.scm b/net/ricketyspace/sicp/two/seven.scm
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+++ b/net/ricketyspace/sicp/two/seven.scm
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+;;;; Under Creative Commons Attribution-ShareAlike 4.0
+;;;; International. See
+;;;; <https://creativecommons.org/licenses/by-sa/4.0/>.
+
+(define-module (net ricketyspace sicp two seven)
+  #:export (make-interval
+            lower-bound
+            upper-bound
+            add-interval))
+
+(define (make-interval a b) (cons a b))
+
+(define (lower-bound x) (car x))
+(define (upper-bound x) (cdr x))
+
+(define (add-interval x y)
+  (make-interval (+ (lower-bound x) (lower-bound y))
+                 (+ (upper-bound x) (upper-bound y))))