## Diff of /doc/source/overview/rules/backward_chaining.txt[e9291b] .. [d43b93]  Maximize  Restore

### Switch to side-by-side view

```--- a/doc/source/overview/rules/backward_chaining.txt
+++ b/doc/source/overview/rules/backward_chaining.txt
@@ -98,8 +98,8 @@

These rules_ are not used until you ask pyke to prove_ a goal.

-The easiest way
-to do this is with pyke.prove_1_ or pyke.prove_n_.  Prove_1_ only
+The easiest way to do this is with
+*some_engine*.prove_1_ or *some_engine*.prove_n_.  Prove_1_ only
returns the first proof found and then stops (or raises pyke.CanNotProve).
Prove_n_ is a generator that generates all possible proofs (which, in
some cases, might be infinite).  In both cases, you pass a tuple of
@@ -115,13 +115,13 @@
========================

>>> import pyke
-    >>> pyke.assert_('family', 'son_of', ('michael', 'bruce', 'marilyn'))
-    >>> pyke.assert_('family', 'son_of', ('bruce', 'thomas', 'norma'))
-    >>> pyke.assert_('family', 'daughter_of', ('norma', 'allen', 'ismay'))
-    >>> pyke.activate('bc_example')
-    >>> for vars, no_plan in pyke.prove_n('bc_example', 'child_parent',
-    ...                                   ('michael',), 4):
+    >>> engine = pyke.engine('examples')
+    >>> engine.assert_('family', 'son_of', ('michael', 'bruce', 'marilyn'))
+    >>> engine.assert_('family', 'son_of', ('bruce', 'thomas', 'norma'))
+    >>> engine.assert_('family', 'daughter_of', ('norma', 'allen', 'ismay'))
+    >>> engine.activate('bc_example')
+    >>> for vars, no_plan in engine.prove_n('bc_example', 'child_parent',
+    ...                                     ('michael',), 4):
...     print vars
('bruce', (), 'son', 'father')
('marilyn', (), 'son', 'mother')
```