1. Skolkovo Institute of Science and Technology, 143026 Skolkovo, Russia
2. Laboratory of Combinatorial and Geometric Structures, Moscow Institute of Physics and Technology, 141700 Dolgoprudny, Russia
3. Caucasus Mathematical Centre, Adyghe State University, 385000 Maikop, Russia
4. Institut de Mathématiques, Université de Neuchâtel, 2000 Neuchâtel, Switzerland