Affiliation: | 1. School of Mathematical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China;2. Lehrstuhl C für Mathematik, RWTH Aachen University, 52056 Aachen, Germany;3. Lehrstuhl C für Mathematik, RWTH Aachen University, 52056 Aachen, Germany;4. School of Mathematics and Information Science, Henan Normal University, Xinxiang, Henan 453007, China |