An algorithm for calculating the difference, intersection,
exclusive-or or union of arbitrary polygon sets.

Copyright: (C) 1997-2004, Advanced Interfaces Group,
	University of Manchester.

	This software is free for non-commercial use. It may be copied,
	modified, and redistributed provided that this copyright notice
	is preserved on all copies. The intellectual property rights of
	the algorithms used reside with the University of Manchester
	Advanced Interfaces Group.

	You may not use this software, in whole or in part, in support
	of any commercial product without the express consent of the
	author.

Author: Alan Murta (email: gpc@cs.man.ac.uk)

WWW:	http://www.cs.man.ac.uk/~toby/alan/software/

	Software documentation at
WWW:	http://www.cs.man.ac.uk/~toby/alan/software/gpc.html