Institution: | 1.School of Mathematics and Statistics, Zhoukou Normal University, Zhoukou, Henan, People’s Republic of China ;2.Mathematics Department, TOBB University of Economics and Technology, 06560, S?güt?zü, Ankara, Turkey ;3.Dipartimento di Matematica e Fisica “Ennio De Giorgi”, Università del Salento, Lecce, Italy ; |