Affiliation: | School of Mathematical Sciences, University of KwaZulu-Natal, Private X01, 3209 Pietermaritzburg, South Africa ; Fachbereich Mathematik, TU Kaiserslautern, Erwin-Schroedinger-Str. 48, D-67663 Kaiserslautern, Germany ; Department of Mathematics, University of Ferrara, Via Machiavelli 35, I-44100 Ferrara, Italy ; Fachbereich Mathematik, TU Kaiserslautern, Erwin-Schroedinger-Str. 48, D-67663 Kaiserslautern, Germany |