Affiliation: | 1.Department of Mathematics, Beijing Jiaotong University, Beijing, 100044, People’s Republic of China ;2.Department of Mathematics, Urmia University, Urmia, 57135, Iran ;3.Department of Mathematics, University of Mazandaran, Babolsar, Iran ;4.Department of Mathematics, Khoy Branch, Islamic Azad University, Khoy, 58168-44799, Iran ; |