A Python set class that lets you work with complements. See the discussion
at the following URI for the background & aims of this class:

  http://mail.python.org/pipermail/python-dev/2006-May/064977.html

The subject came up again recently here:

  http://mail.python.org/pipermail/python-ideas/2009-July/005219.html


I'm releasing this into the public domain in the hope that someone else
will take it and run with it.  You should regard it as a proof of concept,
not a finished product. The code is pretty crufty and the test suite is
very minimal.  It all dates from a time when I was relatively new to
Python.

Having said all that, the code does work :-)

I'd be happy to be kept in the loop if there is any effort to improve this.

Terry Jones
terry@jon.es
July 24, 2009
