Fix grammar (it's -> its).
diff --git a/Doc/ref/ref2.tex b/Doc/ref/ref2.tex
index 68f6570..950a732 100644
--- a/Doc/ref/ref2.tex
+++ b/Doc/ref/ref2.tex
@@ -349,7 +349,7 @@
\item[\code{__*__}]
System-defined names. These names are defined by the interpreter
- and it's implementation (including the standard library);
+ and its implementation (including the standard library);
applications should not expect to define additional names using this
convention. The set of names of this class defined by Python may be
extended in future versions.