--- a/model/ProvenanceModel.html	Fri Aug 05 10:09:49 2011 +0100
+++ b/model/ProvenanceModel.html	Fri Aug 05 10:14:09 2011 +0100
@@ -1007,6 +1007,11 @@
 </ul>
 </p>
 
+<p> The union of two accounts can be defined by forming a container
+containing the unions of their respective constructs. Accounts are not
+closed under union because the constraints may no longer be satisfied
+in the resulting union.  </p>
+
 </section>
 
 <section id="concept-Collection">