1. Institute of Mathematics, Uzbek Academy of Sciences, 29, F. Hodjaev Street, Tashkent 100125, Uzbekistan
2. Department of Mathematics, Analysis, Logic and Discrete Mathematics Ghent University, Ghent, Belgium
3. Department of Mathematics, Aden University, Khormaksar, P.O. Box 6014, Yemen
4. Université de Sousse, Institut Supérieur d'Informatique et des Techniques de Communication, H. Sousse 4000, Tunisia
5. Department of Mathematics and Applied Mathematics, Sefako Makgatho Health Sciences University, Ga-Rankuwa, South Africa
6. China Medical University Hospital, China Medical University, Taichung 40402, Taiwan