%  UNDERBR.STY
\RequirePackage{calc}

\newcommand{\underbracket}[1]
{\mathop{\vtop{\m@th\ialign{##\crcr
 $\hfil\displaystyle{#1}\hfil$\crcr
 \noalign{\kern3\p@\nointerlineskip}%
 \upbracketfill\crcr\noalign{\kern3\p@}}}}\limits}

\newcommand{\upbracketfill}
{\rule{0.8pt}{1ex}%
\leaders\vrule height0.8pt \hfill%
\rule{0.8pt}{1ex}}