Affiliation: | a Department of Mathematics and Statistics, University of Victoria, Victoria, British Columbia V8W 3R4, Canadab Department of Mathematics, University of Osijek, Trg. Ljudevita Gaja 6, HR-31000 Osijek, Croatiac Faculty of Maritime Studies, University of Rijeka, Studentska 2, HR-51000 Rijeka, Croatiad Department of Mathematics and Statistics, Jai Narain Vyas University, Jodhpur 342004, Rajasthan, India |