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%%  Example 01-22-5 
%%  Copyright (C) 2017 Herbert Voss
%% 
%% ==== 
% Show page(s) 1
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\documentclass[]{screxa}
\pagestyle{empty}
\setlength\textwidth{182.31393pt}

%StartShownPreambleCommands
\makeatletter
\let\itemOld\item
\renewcommand\item[1][]{%
  \def\@tempa{#1}
  \ifx\@tempa\@empty\itemOld
  \else\boldmath\itemOld[#1]\unboldmath
  \fi}
\makeatother
\let\sectionOld\section
\renewcommand\section[2][\empty]{%
  \boldmath\sectionOld[#1]{#2}\unboldmath}
%StopShownPreambleCommands
\begin{document}
\section{The math function $f(x)=x^2$}
\begin{description}
\item[This is $y=f(x)$] Only a demonstration.
\item[And $z=f(x,y)$] Another demonstration.
\end{description}
\end{document}
