%% 
%%  An UIT Edition example
%% 
%%  Example 06-15-3 on page 118.
%% 
%%  Copyright (C) 2010 Herbert Voss
%% 
%%  It may be distributed and/or modified under the conditions
%%  of the LaTeX Project Public License, either version 1.3
%%  of this license or (at your option) any later version.
%% 
%%  See http://www.latex-project.org/lppl.txt for details.
%% 
%% 
%% ==== 
% Show page(s) 1
%% 
\documentclass[]{exaarticle}
\pagestyle{empty}
\setlength\textwidth{375.57637pt}
\AtBeginDocument{\setlength\parindent{0pt}
\fboxsep=0pt}
\StartShownPreambleCommands
\usepackage{amsmath,tabularx}
\makeatletter
\def\cs#1{\texttt{\$\textbackslash#1\$}}
\def\mapstofill@{\arrowfill@{\mapstochar\relbar}\relbar\rightarrow}
\newcommand*\xmapsto[6][]{\ext@arrow #3#4#5#6\mapstofill@{#1}{#2}}
\makeatother
\StopShownPreambleCommands
\begin{document}
\begin{tabularx}{\linewidth}{@{}XX@{}}
\cs{ext@arrow 0000}\quad{\large  $\xmapsto[\fbox{-below-}]{\fbox{above}}0000$}
&\cs{ext@arrow 9000}\quad{\large $\xmapsto[\fbox{-below-}]{\fbox{above}}9000$}\\
%
\cs{ext@arrow 0900}\quad{\large  $\xmapsto[\fbox{-below-}]{\fbox{above}}0900$}
&\cs{ext@arrow 0090}\quad{\large $\xmapsto[\fbox{-below-}]{\fbox{above}}0090$}\\
%
\cs{ext@arrow 0009}\quad{\large  $\xmapsto[\fbox{-below-}]{\fbox{above}}0009$}
&\cs{ext@arrow 0099}\quad{\large $\xmapsto[\fbox{-below-}]{\fbox{above}}0099$}\\
%
\cs{ext@arrow 9999}\quad{\large  $\xmapsto[\fbox{-below-}]{\fbox{above}}9999$}
\end{tabularx}
\end{document}