fixes #861 (#1035)

Author: martin-henz

static/img_javascript/ex-3-13-sol.png

@@ -832,6 +832,17 @@ list_ref(z, 100);
       </JAVASCRIPT>
     </SPLITINLINE>
     <LABEL NAME="ex:make-cycle"/>
+    <SOLUTION>
+      (provided by GitHub user jonathantorres)
+      If we try to compute <JAVASCRIPTINLINE>last_pair(z)</JAVASCRIPTINLINE>, the
+      program will enter in a infinite loop, since the end of the list points back
+      to the beginning.
+
+      <FIGURE src="img_javascript/ex-3-13-sol.png">
+	<LABEL NAME= "ex:3-13-sol"/>
+      </FIGURE>
+
+    </SOLUTION>
   </EXERCISE>
 
   <EXERCISE>