1. Department of Computer Science, National University of Singapore, 13 Computing Drive, COM1, Singapore 117417, Republic of Singapore. sanjay@comp.nus.edu.sg
2. Department of Computer Science, University of Auckland, Private Bag 92019, Auckland, New Zealand. bmk@cs.auckland.ac.nz
3. Department of Mathematics and Department of Computer Science, National University of Singapore, 10 Lower Kent Ridge Road, S17, Singapore 119076, Republic of Singapore. fstephan@comp.nus.edu.sg