diff --git a/books/bookvol10.3.pamphlet b/books/bookvol10.3.pamphlet
index e685996..ad36c9b 100644
--- a/books/bookvol10.3.pamphlet
+++ b/books/bookvol10.3.pamphlet
@@ -97007,6 +97007,22 @@ PermutationGroup(S:SetCategory): public == private where
 \end{chunk}
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \section{domain HACKPI Pi}
+What is the purpose of the HACKPI domain?
+
+HACKPI is a hack provided for the benefit of the axiom interpreter.
+As a mathematical type, it is the simple transcendental extension
+Q(\pi) of the rational numbers. This type allows interactive users
+to use the name '%pi' without a type both where a numerical value is expected 
+[ as in draw(sin x,x=-%pi..%pi) ] or when the exact symbolic value is meant.
+The interpreter defaults a typeless %pi to HACKPI and then uses the various
+conversions to cast it further as required by the context.
+
+One could argue that it is unfair to single %pi out from other constants,
+but it occurs frequently enough in school examples (specially for graphs)
+so it was worth a special hack. In a non-interactive environment (library),
+HACKPI would not exist.
+
+(Manuel Bronstein)
 
 \begin{chunk}{Pi.input}
 )set break resume
diff --git a/books/bookvol4.pamphlet b/books/bookvol4.pamphlet
index c0f199d..8f8a5bc 100644
--- a/books/bookvol4.pamphlet
+++ b/books/bookvol4.pamphlet
@@ -331,6 +331,23 @@ November 10, 2003 ((iHy))
 \eject
 \pagenumbering{arabic}
 \setcounter{chapter}{0} % Chapter 1
+\section{What is the purpose of the HACKPI domain?}
+
+HACKPI is a hack provided for the benefit of the axiom interpreter.
+As a mathematical type, it is the simple transcendental extension
+Q(\pi) of the rational numbers. This type allows interactive users
+to use the name '%pi' without a type both where a numerical value is expected 
+[ as in draw(sin x,x=-%pi..%pi) ] or when the exact symbolic value is meant.
+The interpreter defaults a typeless %pi to HACKPI and then uses the various
+conversions to cast it further as required by the context.
+
+One could argue that it is unfair to single %pi out from other constants,
+but it occurs frequently enough in school examples (specially for graphs)
+so it was worth a special hack. In a non-interactive environment (library),
+HACKPI would not exist.
+
+(Manuel Bronstein)
+
 \section{How Axiom Builds}
 \subsection{The environment variables}
 Axiom uses a tree of Makefiles to build the system. Each Makefile
@@ -408,6 +425,12 @@ XLIB=/usr/X11R6/lib
 ZIPS=/research/test/zips
 \end{verbatim}
 
+\section{The runtime structure of Axiom}
+\begin{center}
+\includegraphics{architecture.eps}\\
+{\bf Runtime Structure}
+\end{center}
+
 \subsection{The build step}
 This shows the steps taken to build Axiom in the sequence they happen.
 Each level of indentation is another level of Makefile being executed.
diff --git a/changelog b/changelog
index cd4c232..c61ebae 100644
--- a/changelog
+++ b/changelog
@@ -1,3 +1,5 @@
+20140613 tpd src/axiom-website/patches.html 20140613.03.tpd.patch
+20130613 tpd books/bookvol4,vol10.3 What is the purpose of the HACKPI domain?
 20140613 tpd src/axiom-website/patches.html 20140613.02.tpd.patch
 20140613 tpd books/ProvingAxiomCorrect state the problem
 20140613 tpd src/axiom-website/patches.html 20140613.01.tpd.patch
diff --git a/src/axiom-website/patches.html b/src/axiom-website/patches.html
index ec59716..49808ea 100644
--- a/src/axiom-website/patches.html
+++ b/src/axiom-website/patches.html
@@ -4424,6 +4424,8 @@ books/bookvolbib add Proving Axiom Correct section, Bert04
 books/ProvingAxiomCorrect created
 <a href="patches/20140613.02.tpd.patch">20140613.02.tpd.patch</a>
 books/ProvingAxiomCorrect state the problem
+<a href="patches/20140613.03.tpd.patch">20140613.03.tpd.patch</a>
+books/bookvol4,vol10.3 What is the purpose of the HACKPI domain?
  </body>
 </html>