\def\lline{\bgroup\def\linet@mp{\aftergroup\box\aftergroup0\aftergroup\egroup\bgroup\aftergroup\hss\aftergroup\egroup}\afterassignment\linet@mp\setbox0\hbox to \hsize}
\def\rline{\bgroup\def\linet@mp{\aftergroup\box\aftergroup0\aftergroup\egroup\hss\bgroup\aftergroup\egroup}\afterassignment\linet@mp\setbox0\hbox to \hsize}
\def\lline{\bgroup\def\linet@mp{\aftergroup\box\aftergroup0\aftergroup\egroup\bgroup\aftergroup\hss\aftergroup\egroup}\afterassignment\linet@mp\setbox0\hbox to \hsize}
\def\rline{\bgroup\def\linet@mp{\aftergroup\box\aftergroup0\aftergroup\egroup\hss\bgroup\aftergroup\egroup}\afterassignment\linet@mp\setbox0\hbox to \hsize}