diff --git a/reference/trader/book.xml b/reference/trader/book.xml
index e7dc5fb894..0e25baf44b 100644
--- a/reference/trader/book.xml
+++ b/reference/trader/book.xml
@@ -8,7 +8,7 @@
  <preface xml:id="intro.trader">
   &reftitle.intro;
   <para>
- The trader extension is dedicated for trading software developers requiring to perform technical analysis of financial market data.
+   The trader extension is dedicated for trading software developers requiring to perform technical analysis of financial market data. Extended documentation about indexes, formulas and implementations in other programming languages can be found under <link xlink:href="http://tadoc.org/">tadoc.org</link>.
   </para>
  </preface>