Introduce copy by slicing, used in later chapters.
diff --git a/Doc/tutorial/introduction.rst b/Doc/tutorial/introduction.rst
index 1d67ed3..c953394 100644
--- a/Doc/tutorial/introduction.rst
+++ b/Doc/tutorial/introduction.rst
@@ -523,6 +523,12 @@
>>> 3*a[:3] + ['Boo!']
['spam', 'eggs', 100, 'spam', 'eggs', 100, 'spam', 'eggs', 100, 'Boo!']
+All slice operations return a new list containing the requested elements. This
+means that the following slice returns a shallow copy of the list *a*::
+
+ >>> a[:]
+ ['spam', 'eggs', 100, 1234]
+
Unlike strings, which are *immutable*, it is possible to change individual
elements of a list::