%%
%% The LaTeX Companion, 3ed
%%
%% Example 11-5-18 on page II-190 in "underoverlap --- Partly overlapping horizontal 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{underoverlap,abraces}
\newUOLdecorator\rightunderbrace{\aunderbrace[l4D1r]{#1}}
\UOLaugment\underline
\UOLaugment\overleftarrow \UOLaugment\overrightarrow
%StopShownPreambleCommands

\begin{document}
\[ \underline{a +}[b] \overrightarrow{+}[c + d]
   \rightunderbrace{+ e +}[f] \overleftarrow{+ g}
\]
\end{document}