1. School of Computer Science, McGill University, Montreal, Canada.
2. Department of Mathematics, Massachusetts Institute of Technology, Cambridge, Massachusetts.
3. Department of Computer Science and AI Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts.
4. Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts.
5. Institut für Informatik, Albert-Ludwigs-Universität, Freiburg, Germany.
6. Department of Computer Science and IZBI, University of Leipzig, Leipzig, Germany.