Affiliation: | 1. School of Mathematics and Computer Science, Shanxi Normal University, Linfen, Shanxi 041004, People’s Republic of China;2. Department of Mathematics, Texas A&M University-Kingsville, Kingsville, TX 78363-8202, USA;3. Departamento de Análise Matemática, Facultade de Matemáticas, Universidade de Santiago de Compostela, Santiago de Compostela, Spain |