%% 
%%  Example 02-14-2 
%%  Copyright (C) 2016 Herbert Voss
%% 
%% ==== 
% Show page(s) 1
%% 
%% 
\documentclass[]{screxa}
\pagestyle{empty}
\setlength\textwidth{328.62788pt}
\setlength\parindent{0pt}
\fboxsep=0pt
%StartShownPreambleCommands
\usepackage{amsmath}
\makeatletter
\def\mapstofill@{%
  \arrowfill@{\mapstochar\relbar}\relbar\rightarrow}
\newcommand*\xmapsto[6][]{%
  \ext@arrow #3#4#5#6\mapstofill@{#1}{#2}}
\makeatother
%StopShownPreambleCommands
\begin{document}
\verb+$\ext@arrow 0000$+\quad{\huge $\xmapsto[\fbox{under}]{\fbox{over}}0000$}\par
\verb+$\ext@arrow 9000$+\quad{\huge $\xmapsto[\fbox{under}]{\fbox{over}}9000$}\par
\verb+$\ext@arrow 0900$+\quad{\huge $\xmapsto[\fbox{under}]{\fbox{over}}0900$}\par
\verb+$\ext@arrow 0009$+\quad{\huge $\xmapsto[\fbox{under}]{\fbox{over}}0009$}\par
\verb+$\ext@arrow 0090$+\quad{\huge $\xmapsto[\fbox{under}]{\fbox{over}}0090$}\par
\verb+$\ext@arrow 0099$+\quad{\huge $\xmapsto[\fbox{under}]{\fbox{over}}0099$}\par
\verb+$\ext@arrow 9999$+\quad{\huge $\xmapsto[\fbox{under}]{\fbox{over}}9999$}
\end{document}
