% 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}}