Co-operation is...

An aye for an aye and a truth for a truth.

I had hoped that this phrase was a Magree original, but there are at least two prior occurrences on the web.

http://www.glib.com/botb_05-14-01.html

http://listserv.uts.edu.au/archives/sys-func/2007-July/009080.html

See also http://wiki.answers.com/Q/What_are_some_examples_of_epigrams