%% 
%%  Der Mathematiksatz mit LaTeX, 1. Auflage 2009
%% 
%%  Example 6-15-3 on page 126.
%% 
%%  Copyright (C) 2009 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.
%% 

\documentclass[]{ttctexa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{355.65944pt}
\AtBeginDocument{\setlength\parindent{0pt}
\fboxsep=0pt}
\StartShownPreambleCommands
\usepackage{amsmath,tabularx}
\makeatletter
\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@{}}
\verb+$\ext@arrow 0000$+\quad{\large  $\xmapsto[\fbox{-unten-}]{\fbox{oben}}0000$}
&\verb+$\ext@arrow 9000$+\quad{\large $\xmapsto[\fbox{-unten-}]{\fbox{oben}}9000$}\\
%
\verb+$\ext@arrow 0900$+\quad{\large  $\xmapsto[\fbox{-unten-}]{\fbox{oben}}0900$}
&\verb+$\ext@arrow 0009$+\quad{\large $\xmapsto[\fbox{-unten-}]{\fbox{oben}}0009$}\\
%
\verb+$\ext@arrow 0090$+\quad{\large  $\xmapsto[\fbox{-unten-}]{\fbox{oben}}0090$}
&\verb+$\ext@arrow 0099$+\quad{\large $\xmapsto[\fbox{-unten-}]{\fbox{oben}}0099$}\\
%
\verb+$\ext@arrow 9999$+\quad{\large  $\xmapsto[\fbox{-unten-}]{\fbox{oben}}9999$}
\end{tabularx}
\end{document}