Department of Computer Science, University of Western Ontario, London, ON, Canada. ilie@csd.uwo.ca|Department of Computer Science, University of Western Ontario, London, ON, Canada. ilie@csd.uwo.ca|Department of Computer Science, University of Western Ontario, London, ON, Canada. ilie@csd.uwo.ca|Department of Computer Science, University of Western Ontario, London, ON, Canada. ilie@csd.uwo.ca