/usr/lib/gerris/gfs2tex.py is in gerris 20110329-dfsg.2-1build1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gerris/../../share/gerris/lib/gfs2tex.py
/usr/lib/gerris/../../share/gerris/lib/gfs2tex.py