1 Scientific and Educational Mathematical Center "Mathematics of Future Technologies," Lobachevsky State University of Nizhny Novgorod, 23 Gagarina Ave., 603950 Nizhny Novgorod, Russia.
2 National Research University Higher School of Economics, 25/12 Bolshaya Pecherskaya Ulitsa, 603155 Nizhny Novgorod, Russia.
3 Neuroscience Institute and Department of Mathematics and Statistics, Georgia State University, 100 Piedmont Ave., Atlanta, Georgia 30303, USA.