H
g/^/s/@BEGCH@/\\tdBCOL{/
g/^/s/@ENDCH@/\
\\tdECOL}/
g/^\\tdBCOL/.,/^\\tdECOL}$/-1s/\$/\\tdECOL}\$\\tdBCOL{/g
g/^/s/\\tdBCOL{\\tdECOL}//g
/\\startexdiff/ a
\newcommand{\tdBCOL}[1]{{\bf #1 }}
\newcommand{\tdECOL}{}
.
1,$p
q

Written by Hugo Krawczyk, May 1993.