diff --git a/tutorial/09.markdown b/tutorial/09.markdown
index 361a58c..f82c373 100644
--- a/tutorial/09.markdown
+++ b/tutorial/09.markdown
@@ -1,8 +1,8 @@
 The next data structure that we'll look at is a set. A set is similar to a
 list, except it does not have a specific order and each element may only appear
-once. Both the data structures are very useful because while in a list
-is fast to access the elements near the top or the bottom, and the order of
-the elements is preserved, in a set is very fast to test for membership, that
+once. Both the data structures are very useful because a list
+is fast when accessing the elements near the top or the bottom and the order of
+the elements is preserved; while a set is very fast to test for membership, that
 is, to immediately know if a given element was added or not. Moreover in
 a set a given element can exist only in a single copy.