Add some cross-references to the docs. Simplify the python code equivalent for zip(). Supply an optional argument for the nth() recipe.
diff --git a/Lib/test/test_itertools.py b/Lib/test/test_itertools.py
index 8492484..cf0ca24 100644
--- a/Lib/test/test_itertools.py
+++ b/Lib/test/test_itertools.py
@@ -1419,9 +1419,9 @@
... "Return function(0), function(1), ..."
... return map(function, count(start))
->>> def nth(iterable, n):
-... "Returns the nth item or None"
-... return next(islice(iterable, n, None), None)
+>>> def nth(iterable, n, default=None):
+... "Returns the nth item or a default value"
+... return next(islice(iterable, n, None), default)
>>> def quantify(iterable, pred=bool):
... "Count how many times the predicate is true"