Affiliation: | Institut für Mathematik, Universität Paderborn, Warburger Str. 100, 33098 Paderborn, Germany;College of Mathematics and Statistics, Chongqing University, Chongqing 401331, PR China;School of Mathematics and Statistics Science, Ludong University, Yantai 264025, PR China;Department of Applied Mathematics, Chongqing University of Posts and Telecommunications, Chongqing 400065, PR China |