%% 
%%  Ein Beispiel der DANTE-Edition
%%  Mathematiksatz mit LaTeX
%%  3. Auflage
%%  Beispiel 11-02-1 auf Seite 240.
%%  Copyright (C) 2018 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[10pt]{exaartplain}
\pagestyle{empty}
\setlength\textwidth{146.40707pt}
\setlength\parindent{0pt}
%StartShownPreambleCommands
\DeclareMathVersion{foo}
\SetMathAlphabet{\mathbf}{foo}{OMS}{cmsy}{m}{n}
\DeclareMathAlphabet{\mathxy}{OT1}{lmr}{bx}{n}
\SetMathAlphabet{\mathxy}{foo}{OT1}{}{}{}
%StopShownPreambleCommands
\begin{document}
[$ \mathbf{y=f(x)}   $] [(bold)
\mathversion{bold}   $ \mathbf{y=f(x)} $] [(foo)
\mathversion{foo}    $ \mathbf{y=f(x)} $
                     $ \mathxy{y=f(x)} $] [(normal)
\mathversion{normal} $ \mathbf{y=f(x)} $]
\end{document}