Document that sys.builtin_module_names is now a tuple.
diff --git a/Doc/lib/libsys.tex b/Doc/lib/libsys.tex
index ff5d65e..32f6699 100644
--- a/Doc/lib/libsys.tex
+++ b/Doc/lib/libsys.tex
@@ -19,7 +19,7 @@
\end{datadesc}
\begin{datadesc}{builtin_module_names}
- A list of strings giving the names of all modules that are compiled
+ A tuple of strings giving the names of all modules that are compiled
into this Python interpreter. (This information is not available in
any other way --- \code{sys.modules.keys()} only lists the imported
modules.)