Affiliation: | (1) Department of Mathematics, University of Alberta, TEG 2G1 Edmonton, Alberta, Canada;(2) National Research Institute for Mathematical Sciences CSIR, P.O. Box 395, Pretoria, Republic of South Africa;(3) Department of Mathematics, The Ohio State University, 43210 Columbus, Ohio, USA;(4) Bolyai Institute, József Attila University, Aradi vértanúk Tere 1, H-6720 Szeged |