--- a/primer/Primer.html	Thu Dec 01 14:43:48 2011 +0000
+++ b/primer/Primer.html	Thu Dec 01 15:43:37 2011 +0000
@@ -292,11 +292,13 @@
     </p>
     <p>
      In PROV-DM, we say there is <i>complementarity</i> between one entity and another
-     if everything that characterizes the second is also true of the first.
+     if, in some period of time, they have the same or compatible characterization.
      So, both "the second version of document D" and "document D as stored on my filesystem"
-     are complements of "document D", because they are both more specific characterizations
-     of D. If a version of D stored on my filesystem is the second one, then
-     "document D as stored on my filesystem" is a complement of "the second version of document D".
+     are complements of "document D", because they are both characterized by being
+     document D, but with specific additional attributes.
+     If, at some point in time, a version of D stored on my filesystem is the second one, then
+     "document D as stored on my filesystem" and "the second version of document D" are
+     complements of each other.
     </p>
 
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