1. V.I. Romanovskiy Institute of Mathematics, Uzbekistan Academy of Sciences, 9 University Street, 100174 Tashkent, Uzbekistan
2. CMA-UBI, Universidade da Beira Interior, Covilhã, Portugal
3. National University of Uzbekistan, Tashkent 100170, Uzbekistan
4. Department of Physics and Mathematics, Urgench State University, Kh. Alimdjan Street, 14, Urganch 220100, Uzbekistan