[1] Univ Twente, Fac EEMCS, NL-7500 AE Enschede, Netherlands
[2] Stevens Inst Technol, Dept Math Sci, Hoboken, NJ 07030 USA
[3] London Sch Econ, Dept Math, London WC2A 2AE, England
[4] Seton Hall Univ, Dept Math & Comp Sci, S Orange, NJ 07079 USA
[5] San Jose State Univ, Dept Math, San Jose, CA 95192 USA
[6] Univ Nottingham, Sch Math Sci, Nottingham NG7 2RD, England
[7] Penn State Univ, Dept Math, Media, PA 19063 USA