%  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}}