[1] Masaryk Univ, Fac Informat, Botanicka 68A, Brno 60200, Czech Republic
[2] Univ Warwick, Math Inst, DIMAP, Coventry CV4 7AL, W Midlands, England
[3] Univ Warwick, Dept Comp Sci, Coventry CV4 7AL, W Midlands, England
[4] Univ Victoria, Dept Math & Stat, David Turpin Bldg A425,3800 Finnerty Rd, Victoria, BC V8P 5C2, Canada
[5] Univ Warwick, Math Inst, Coventry CV4 7AL, W Midlands, England
[6] Univ Warwick, DIMAP, Coventry CV4 7AL, W Midlands, England
[7] McGill Univ, Dept Math & Stat, Montreal, PQ, Canada
[8] Czech Tech Univ, Fac Nucl Sci & Phys Engn, Dept Math, Trojanova 13, Prague 12000, Czech Republic
[9] Princeton Univ, Dept Math, Princeton, NJ 08544 USA
[10] Inst Adv Study, Sch Math, Princeton, NJ USA