fixes #880 (#1037)

Author: martin-henz

xml/chapter4/section3/subsection1.xml

@@ -648,6 +648,18 @@ function a_pythogorean_triple_between(low, high) {
 }
       </JAVASCRIPT>
     </SNIPPET>
+    <SOLUTION>
+      <SNIPPET>
+	<JAVASCRIPT>
+// solution by GitHub user jonathantorres
+
+function an_integer_between(low, high) {
+    require(low &lt;= high);
+    return amb(low, an_integer_between(low+1, high));
+}
+	</JAVASCRIPT>
+      </SNIPPET>
+    </SOLUTION>
   </EXERCISE>
 
   <EXERCISE>