1. Faculty of Mechanics and Mathematics, Lomonosov Moscow State University, Moscow 119234, Russia
2. “Vega” Institute, Moscow 119234, Russia
3. Moscow School of Economics, Lomonosov Moscow State University, Moscow 119234, Russia
4. Laboratoire de Mathématiques, Université de Franche-Comté, 16 Route de Gray, 25030 Besançon, France