minor markup adjustments
diff --git a/Doc/lib/libweakref.tex b/Doc/lib/libweakref.tex
index fc88916..c8d82a8 100644
--- a/Doc/lib/libweakref.tex
+++ b/Doc/lib/libweakref.tex
@@ -57,7 +57,7 @@
Return a weak reference to \var{object}. The original object can be
retrieved by calling the reference object if the referent is still
alive; if the referent is no longer alive, calling the reference
- object will cause \code{None} to be returned. If \var{callback} is
+ object will cause \constant{None} to be returned. If \var{callback} is
provided and not \constant{None},
it will be called when the object is about to be
finalized; the weak reference object will be passed as the only
@@ -191,7 +191,7 @@
\end{verbatim}
If the referent no longer exists, calling the reference object returns
-\code{None}:
+\constant{None}:
\begin{verbatim}
>>> del o, o2