Add MutableSet example.
diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst
index b136cf1..4e79e25 100644
--- a/Doc/library/collections.rst
+++ b/Doc/library/collections.rst
@@ -132,7 +132,12 @@
inherit from both :meth:`Set` and :meth:`Hashable`, then define
``__hash__ = Set._hash``.
-(For more about ABCs, see the :mod:`abc` module and :pep:`3119`.)
+.. seealso::
+
+ * `OrderedSet recipe <http://code.activestate.com/recipes/576694/>`_ for an
+ example built on :class:`MutableSet`.
+
+ * For more about ABCs, see the :mod:`abc` module and :pep:`3119`.
:class:`Counter` objects