1. Department of Computer Science, New Jersey Institute of Technology, Newark, NJ, USA. E-mail: crix@njit.edu
2. AT&T Labs – Research, Florham Park, NJ, USA. E-mail: garay@research.att.com
3. Microsoft Research, Redmond, WA, USA. E-mail: senyk@microsoft.com
4. Department of Computer Science, UCLA, Los Angeles, CA, USA. E-mail: rafail@cs.ucla.edu