case $# in
2)	;;
*)   echo "Usage: findrefs in_file out_file" ;
      exit ;;
esac
sed -e '/[[\]]/!d
	s/^[^[\]]*\[/[/
	s/][^[]*/]/g
	s/].*\[/]\
[/g' < $1 \
| sort | uniq > $2