%%
%% The LaTeX Companion, 3ed
%%
%% Example 11-5-9 on page II-184 in "Further horizontal extensions".
%%
%% 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{111.0pt}

  \usepackage{lmodern}

%StartShownPreambleCommands
\usepackage{mathtools}
%StopShownPreambleCommands

\begin{document}
\begin{gather*}
  \overbracket{a+\underbracket{b+\overbrace{c+d\,}\!+e}+f} \\
     \overbracket[1.5pt][3pt]{a+
         \underbracket[3pt][4pt]{b+
            \overbracket[.7pt][2pt]{c+d\,}\!+e}+f}
\end{gather*}
\end{document}