1. Department of Differential Equations, Institute of Mathematics, Ufa Scientific Center, RAS, Chernyshevsky str., 112, Ufa, 450008, Russia
2. Faculty of Physics and Mathematics, Bashkir State Pedagogical University, October rev. st. 3a, Ufa, 450000, Russia
3. Faculty of Science, University of Hradec Králové Rokitanského 62, Hradec Králové, 500 03, Czech Republic
4. Faculty of Mathematics, Technische Universität Chemnitz, Chemnitz, 09107, Germany
5. Technische Universität Hamburg-Harburg, Am Schwarzenberg-Campus 3, Hamburg, 21073, Germany
6. Faculty of Mathematics, Technische Universität Dortmund, Dortmund, 44227, Germany