Typo fix
diff --git a/Doc/lib/libcollections.tex b/Doc/lib/libcollections.tex
index cea06e8..d9bfa39 100644
--- a/Doc/lib/libcollections.tex
+++ b/Doc/lib/libcollections.tex
@@ -310,7 +310,7 @@
When a letter is first encountered, it is missing from the mapping, so the
\member{default_factory} function calls \function{int()} to supply a default
-count of zero. The increment operation then builds of the count for each
+count of zero. The increment operation then builds up the count for each
letter. This technique makes counting simpler and faster than an equivalent
technique using \method{dict.get()}: