%%
%% The LaTeX Companion, 3ed
%%
%% Example 9-3-15 on page I-674 in "Adjusting the font series defaults".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{159.0pt}

  \setlength\parindent{0pt}

%StartShownPreambleCommands
\usepackage{bm}
\newcommand\vbeta{\IfFontSeriesContextTF{bf}%
   {\ensuremath{\bm{\beta}}}{\ensuremath{\beta}}}
%StopShownPreambleCommands

\begin{document}
\section{\vbeta-isotopes}
The \vbeta-isotopes are interesting: $\vbeta$
\end{document}