--- a/doc/tutorial.rst	Tue Jul 28 13:27:13 2009 -0700
+++ b/doc/tutorial.rst	Tue Aug 04 14:28:17 2009 -0700
@@ -70,7 +70,7 @@
 the entire filtration at once, compute its persistence in one operation, and
 then examine the pairings. The second way is to feed simplices one by one in an
 *online* manner and manually keep track of the pairs that are created.
-:class:`ZigzagPersistence` and `CohomologyPersistence` |cpp-only| accept their
+:class:`ZigzagPersistence` and :class:`CohomologyPersistence` accept their
 input this way,
 
 
@@ -123,7 +123,10 @@
 ^^^^^^
 
 Class :class:`ZigzagPersistence` accepts additions and removals of the simplices
-one by one, and returns an internal representation of the simplices. When one
+one by one, and returns an internal representation of the simplices.
+(:class:`CohomologyPersistence` works in the same way, but accepts only
+additions of the simplices.) 
+When one
 adds a simplex via :meth:`ZigzagPersistence.add`, one must provide its boundary
 in this internal representation together with a *birth value* which
 :class:`ZigzagPersistence` will store in case a class is born as a result of the
@@ -161,7 +164,9 @@
 :func:`add_simplices` and :func:`remove_simplices`.
 
 See the :ref:`bindings reference <python-bindings>` for more details, and
-:ref:`triangle-zigzag-example` for an example.
+:ref:`triangle-zigzag-example` for an example of :class:`ZigzagPersistence`.
+See :ref:`rips-pairwise-cohomology` for an example of
+:class:`CohomologyPersistence`.
 
 
 .. _speed-up-suggestions:

--- a/examples/triangle/triangle-zigzag.py	Tue Jul 28 13:27:13 2009 -0700
+++ b/examples/triangle/triangle-zigzag.py	Tue Aug 04 14:28:17 2009 -0700
@@ -30,6 +30,6 @@
 for s in sorted(complex.keys(), reverse = True):
     print "%d: Removing %s" % (b, s)
     d = zz.remove(complex[s], b)
-    complex[s] = None
+    del complex[s]
     if d:   print "Interval (%d, %d)" % (d, b-1)
     b += 1