%%
%% The LaTeX Companion, 3ed
%%
%% Example 9-4-5 on page I-680 in "Defining new alphabet identifiers".
%%
%% 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}
%StartShownPreambleCommands
\DeclareMathAlphabet{\mathsfsl}{T1}{cmss}{m}{sl}
%StopShownPreambleCommands

\begin{document}
We demonstrate this with the formula
\begin{equation}
  \sum \mathsfsl{A}_{i} = a \tan \beta
\end{equation}
\end{document}