% Fichier exo4.15.tex - Ch. Rolland/O Reilly France
\documentclass{article}
\usepackage[latin1]{inputenc}
\begin{document}
$$
\begin{array}{c@{}c@{}c}
\multicolumn{2}{l}{\overbrace{\qquad\qquad}}&\\[-1ex]
a\ +&\ b+c\ &+\ d \\[-2ex]
&\multicolumn{2}{l}{\underbrace{\qquad\qquad}}
\end{array}
$$
\end{document}
