%%
%% The LaTeX Companion, 3ed
%%
%% Example 12-1-10 on page II-230 in "The world of (Latin) math alphabets".
%%
%% 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{201.0pt}

  \AddToHook{begindocument/end}{%      % save some space in the example
    \setlength\abovedisplayshortskip{4pt}%
    \setlength\belowdisplayskip{0pt}%
    \setlength\belowdisplayshortskip{0pt}}

%StartShownPreambleCommands
\usepackage{amsmath}
\DeclareMathAlphabet\mathscr{U}{rsfs}{m}{n}
%StopShownPreambleCommands

\begin{document}
\begin{multline*} \mathscr{ABCDEFGHIJKLM} \\
    \mathscr{NOPQRSTUVWXYZ}  \end{multline*}
\[  \mathcal{ABCDEFGHIJKLMNOPQRSTUVWXYZ}  \]
\end{document}