H
g/^/s/@BEGCH@\(.*\)@ENDCH@/\\tdSM \1/
g/^/s/@BEGCH@/\\tdBM /
g/^/s/@ENDCH@/\\tdEM/
/\\startexdiff/ a
\newcommand{\tdBM}{\marginpar{$\bf{\Downarrow}$}}
\newcommand{\tdEM}{\marginpar{$\bf{\Uparrow}$}}
\newcommand{\tdSM}{\marginpar{$\bf{\Leftrightarrow}$}}
.
1,$p
q

Written by Hugo Krawczyk, May 1993.