--- a/model/prov-constraints.html	Mon Aug 06 10:03:20 2012 +0100
+++ b/model/prov-constraints.html	Mon Aug 06 11:10:35 2012 +0100
@@ -1344,17 +1344,29 @@
     </li></ol>
     </div>
 
-  <div class="remark">In an association of the form
+  <div class="remark">
+<p>In an association of the form
   <span class="name">wasAssociatedWith(id;a, ag,-,attr)</span>, the
   absence of a plan means: either no plan exists, or a plan exists but
   it is not identified.  Thus, it is not equivalent to <span
   class="name">wasAssociatedWith(id;a,ag,p,attr)</span> where a
-  plan <span class="name">p</span> is given.  Similarly, a  <span
+  plan <span class="name">p</span> is given.</p>
+</div>
+  <div class="remark">
+<p> A derivation  <span
   class="name">wasDerivedFrom(id;e2,e1,a,gen,use,attrs)</span> that
-  specifies an activity explicitly is not
-  equivalent to <span
-  class="name">wasDerivedFrom(id;e2,e1,-,gen,use,attrs)</span> with a
-  missing activity.
+  specifies an activity explicitly indicates that  this activity achieved the derivation, with a usage <span
+  class="name">use</span> of entity <span
+  class="name">e1</span>, and a generation <span
+  class="name">gen</span> of entity <span
+  class="name">e2</span>.
+  It differs from a derivation of the form
+   <span
+  class="name">wasDerivedFrom(id;e2,e1,-,-,-,attrs)</span> with 
+  missing activity, generation, and usage. In the latter form, it is not specified
+  if one or more activities are involved in the derivation. </p>
+
+ <p>Note: Let us consider a system, in which a derivation is underpinned by multiple activities. Conceptually, one could also model such a system with a new activity, encompassing the two original activities and underpinning the derivation.   The infererences defined in this specification do not allow the latter modelling to be inferred from the former. Hence, the two  modellings of the same system are regarded as different in the context of this specification.</p>
     </div>
 </section>
     
@@ -1567,7 +1579,7 @@
   class="name">_t1</span> and <span
   class="name">_t2</span> such that  <span
 class="name">used(id1;a,e1,_t1,[])</span> and <span
-class="name">wasGeneratedBy(id2;e2,a,_t2,[])</span> hold.
+class="name">wasGeneratedBy(id2;e2,a,_t2,[])</span>.
 </p>
 </div>
 <p>
@@ -1584,27 +1596,37 @@
 class='conditional'>THEN</span> there exist <span
   class="name">_t1</span> and <span class="name">use</span> such
   that <span class="name">used(use;a,e1,_t1,[])</span> and <span
-  class="name">wasDerivedFrom(id;e2,e1,a,gen,use,attrs)</span> hold.
+  class="name">wasDerivedFrom(id;e2,e1,a,gen,use,attrs)</span>.
 </div>
 <p>This inference is justified by the fact that the entity denoted by <span class="name">e2</span> is generated by at most one activity
 (see <a class="rule-text" href="#unique-generation"><span>TBD</span></a>). Hence,  this activity is also the one referred to by the usage of <span class="name">e1</span>. 
 </p>
 
 
-<div class="remark">
-  <p>The converse inference does not hold.  Informally, from <span
-class="name">wasDerivedFrom(id;e2,e1,-,-,-,attrs)</span> and <span
-class="name">used(use;a,e1,_t1,attrs1)</span>, one cannot derive <span
-class="name">wasGeneratedBy(gen;e2,a,_t2,attrs2)</span> because entity <span
-class="name">e1</span> may be used by many activities, whereas at most
-one activity could generate the entity <span class="name">e2</span>.
-Even if <span class="name">e2</span> is used by some activity that
-later generates <span class="name">e1</span> is generated, it is not
-safe to assume that <span class="name">e2</span> was derived from
-<span class="name">e1</span>.  Derivation is not defined to be
-transitive either, following similar reasoning as for <span
-class="name">wasInformedBy</span>. </p>
-
+<div class="remark" id="derivation-generation-use-remark">
+  <p>
+ <a class="rule-text" href="#derivation-use"><span>TBD</span></a> allows a usage to be inferred from a derivation with explicit activity and a generation.  
+
+<p>
+<span class='conditional'>IF</span> 
+<span class="name">wasDerivedFrom(id;e2,e1,a,-,-,attrs)</span>,
+<span class="name">wasGeneratedBy(gen;e2,a,_t2,_attrs2)</span>,
+and <span class="name">used(use;a,e1,_t1,[])</span>, <span
+class='conditional'>IT IS NOT NECESSARILY THE CASE THAT</span> 
+<span
+  class="name">wasDerivedFrom(id;e2,e1,a,gen,use,attrs)</span>.
+
+<p>Indeed,
+<span
+class="name">e1</span> may be used multiple times by 
+ <span class="name">a</span>, usage  <span class="name">use</span>
+may not be involved in the derivation  (for instance, it may well have taken place after 
+the generation of <span
+class="name">e2</span>).</p>
+
+
+<p>Derivation is not defined to be
+transitive either. Applications may define specializations of this relation that are transitive. </p>
   </div>
 
 <hr />
@@ -1615,9 +1637,9 @@
 
 <div class='inference' id='specific-derivation-inference'>
 <p><span class='conditional'>IF</span> <span
-  class="name">wasDerivedFrom(id;e2,e1,_act,_gen,_use,attrs)</span>
-  holds, <span class='conditional'>THEN</span> <span
-  class="name">wasDerivedFrom(id;e2,e1,-,-,-,attrs)</span> holds.
+  class="name">wasDerivedFrom(id;e2,e1,_act,_gen,_use,attrs)</span>, 
+<span class='conditional'>THEN</span> <span 
+  class="name">wasDerivedFrom(id;e2,e1,-,-,-,attrs)</span>.
 </p>
 </div>