diff --git a/xml/chapter4/section3/subsection1.xml b/xml/chapter4/section3/subsection1.xml
index 2740a3395..25eacdae1 100644
--- a/xml/chapter4/section3/subsection1.xml
+++ b/xml/chapter4/section3/subsection1.xml
@@ -648,6 +648,18 @@ function a_pythogorean_triple_between(low, high) {
}
+
+
+
+// solution by GitHub user jonathantorres
+
+function an_integer_between(low, high) {
+ require(low <= high);
+ return amb(low, an_integer_between(low+1, high));
+}
+
+
+