1. V.I.Romanovskiy Institute of Mathematics, Uzbekistan Academy of Sciences, Tashkent, Uzbekistan
2. Department of Mathematics: Analysis, Logic and Discrete Mathematics, Ghent University, Ghent, Belgium
3. School of Mathematical Sciences, Queen Mary University of London, London, UK
4. Al-Farabi Kazakh National University, Almaty, Kazakhstan
5. Institute of Mathematics and Mathematical Modeling, Almaty, Kazakhstan