%%
%% The LaTeX Companion, 3ed
%%
%% Example 11-5-15 on page II-188 in "abraces --- Customizable over and under braces".
%%
%% 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{.3\abovedisplayskip}%
    \setlength\belowdisplayskip{.3\belowdisplayskip}%
  }

%StartShownPreambleCommands
\usepackage{abraces,amsmath}
%StopShownPreambleCommands

\begin{document}
\begin{gather*}
  \aoverbrace [,1,]{(x+y+z)} [a,b]         \\
  \aunderbrace['1']{(x+y+z)} \relax [a,b)
\end{gather*}
\end{document}