Department of Mathematics and Computer Science, Technical University of Eindhoven, Den Dolech 2, Eindhoven, AZ, The Netherlands;CSE, University of New South Wales, Den Dolech 2, Eindhoven, AZ, Australia;Department of Information Engineering and Computer Science, University of Trento, Den Dolech 2, Eindhoven, AZ, Italy;Department of Information Engineering and Computer Science, IBM T.J. Watson Research Center, Den Dolech 2, Hawthorne, AZ, Italy