--- a/README	Mon Aug 01 14:12:48 2011 +0200
+++ b/README	Mon Aug 01 14:28:38 2011 +0200
@@ -146,6 +146,12 @@
 
 state: in progress
 
+This extension introduce the *obsolete* concept. It adds a new *obsolete* relation between two changeset. A relation ``<changeset B> obsolete <changeset A>`` is set to denote that ``<changeset B>`` is new version of ``<changeset A>``
+
+The *obsolete* relation act as a **perpendicular history** to the standard
+changeset history. Standard changeset history versions files. When *obsolete*
+relation versions changeset
+
 Usage and Feature
 ------------------