%%
%% The LaTeX Companion, 3ed
%%
%% Example 12-3-3 on page II-241 in "euler, eulervm --- Accessing Zapf's Euler fonts".
%%
%% 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{87.0pt}
%StartShownPreambleCommands
%\usepackage[mathscr]{eucal} \usepackage{eufrak} % old way
\usepackage[scr=euler,frak=euler]{mathalpha}
%StopShownPreambleCommands

\begin{document}
\[ \mathcal{A} \neq \sum_{k<n} \mathscr{A}_k \neq \mathfrak{A} \]
\end{document}