Affiliation: | a Dept. of Mathematics, University of Missouri, Columbia, MO 65211, USA b Dept. of Mathematics, University of Toronto, Toronto, Ontario M5S 3G3, Canada c Inst. de Matemáticas, Universidad Nacional Autónoma de México, C.P. 58089, Morelia, Michoacán, México d Dept. of Computing, Macquarie University, Sydney, NSW 2109, Australia |