Affiliation: | a School of Mathematical Sciences, University College Dublin, Ireland b Department of Mathematics and Computer Science, Eindhoven University of Technology, Den Dolech 2, 5600 MB Eindhoven, The Netherlands c Microsoft Research, One Microsoft Way, Redmond, WA 98052, USA d Mathematisch Instituut, Universiteit Leiden, Postbus 9512, 2300 RA Leiden, The Netherlands |