Cross reference the set built-ins with the sets module.

Doc/lib/libstdtypes.tex

@@ -1291,6 +1291,14 @@ Note, the non-operator versions of the \method{update()},
 \method{symmetric_difference_update()} methods will accept any iterable
 as an argument.
 
+The design of the set types was based on lessons learned from the
+\module{sets} module.
+     
+\begin{seealso}     
+  \seemodule[comparison-to-builtin-set]{sets}{Differences between
+     the \module{sets} module and the built-in set types.}					      
+\end{seealso}
+     
 
 \subsection{Mapping Types --- class{dict} \label{typesmapping}}
 \obindex{mapping}