%%
%% The LaTeX Companion, 3ed
%%
%% Example 11-4-25 on page II-174 in "braket --- Dirac bra--ket and set notation".
%%
%% 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{tlc3examargin}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{135.0pt}

  % Shorten the vertical size of the example ...
  \AtBeginDocument{%
    \setlength\abovedisplayskip{.1\abovedisplayskip}%
    \setlength\belowdisplayskip{.5\belowdisplayskip}%
  }

%StartShownPreambleCommands
\usepackage{mathtools,braket}
%StopShownPreambleCommands

\begin{document}
\begin{gather*}
 \ket{\psi}\bra{\phi} : \ket{\xi}
       \mapsto    \ket{\psi} \braket{\psi|\xi}           \\
 \Braket{ \phi | \frac{\partial^2}{\partial t^2} | \psi} \\
 \shortintertext{Also:} \Set{ x\in \Re^2 | 0 < |x| < 5 }
\end{gather*}
\end{document}