--- a/doc/source/krb_syntax/bc_rule.txt
+++ b/doc/source/krb_syntax/bc_rule.txt
@@ -1,3 +1,25 @@
+.. $Id$
+.. 
+.. Copyright Š 2007 Bruce Frederiksen
+.. 
+.. Permission is hereby granted, free of charge, to any person obtaining a copy
+.. of this software and associated documentation files (the "Software"), to deal
+.. in the Software without restriction, including without limitation the rights
+.. to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+.. copies of the Software, and to permit persons to whom the Software is
+.. furnished to do so, subject to the following conditions:
+.. 
+.. The above copyright notice and this permission notice shall be included in
+.. all copies or substantial portions of the Software.
+.. 
+.. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+.. IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+.. FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+.. AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+.. LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+.. OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+.. THE SOFTWARE.
+
 restindex
     crumb: Bc_rule
     page-description:
@@ -84,6 +106,12 @@
     name ::= IDENTIFIER
            | '$'IDENTIFIER
 
+Here are the links to the definitions for pattern_ and python_premise_.
+
+If the *bc_premise* includes the ``!``, an exception will be raised if the
+premise fails.  This can help in debugging.  Note that this does not apply
+when backtracking_.
+
 If a single *name* is used in the *bc_premise*,
 the `rule base category`_ for the current `rule base`_ is assumed.
 
@@ -99,8 +127,6 @@
 active_ `rule base`_.  In that case, the derived `rule base`_ is used to
 prove the premise. 
 
-Here are the links to the definitions for pattern_ and python_premise_.
-
 Plan_spec
 ------------
 
@@ -167,6 +193,7 @@
 
 .. _active: ../using_pyke.html#setting-up-each-case
 .. _backward-chaining: ../overview/rules/backward_chaining.html
+.. _backtracking: ../overview/rules/backward_chaining.html#backtracking
 .. _category: `rule base category`_
 .. _fact base: ../overview/knowledge_bases/fact_bases.html
 .. _pattern: pattern.html