--- a/model/ProvenanceModel.html	Wed Sep 14 14:55:13 2011 +0100
+++ b/model/ProvenanceModel.html	Wed Sep 14 14:57:01 2011 +0100
@@ -1690,6 +1690,8 @@
 contains a set of provenance expressions, is asserted by agent  <span class="name">a1</span>, is referred to by identifier <span class="name">v1</span>.
 </p>
 
+<div class='note'>Luc: define well-formed account, and union of two well-formed accounts may not be a well-formed account.</div>
+
 <p> The union of two accounts can be defined by forming a container
 containing the unions of their respective expression. Accounts are not
 closed under union because the