Hi, groff_tmac(5) says
ptx A single macro is provided in this file, xx, for formatting
permuted index entries as produced by the GNU ptx(1) program.
In case you need a different formatting, copy the macro into
your document and adapt it to your needs.
but /usr/share/groff/1.22.3/tmac has no ptx.tmac.
There is a /usr/heirloom/lib/doctools/tmac/ptx from package
heirloom-doctools.
Cheers, Ralph.
