How to tidy up the .keywords file on a gentoo system?

One can select testing packages on a gentoo stable system by adding a line with the following syntax to keywords list: cat /etc/portage/package.keywords =dev-python/ipython-0.13.2 ~amd64 # and many lines later =dev-python/ipython-0.14.1 ~amd64 # and many lines later >=dev-python/ipython-0.13.4 ~amd64 This file will grow within the time and sooner or later one can not remember which lines are obsolete. **How can I tidy up the list with a script from time to time?** A line should be deleted, * if the testing version is already stabilized * >= was used for the same package * = was used for the same package with smaller version number