Fix markup.

Doc/lib/libstdtypes.tex

@@ -1300,7 +1300,7 @@ The design of the set types was based on lessons learned from the
 \end{seealso}
      
 
-\subsection{Mapping Types --- class{dict} \label{typesmapping}}
+\subsection{Mapping Types --- \class{dict} \label{typesmapping}}
 \obindex{mapping}
 \obindex{dictionary}