1. Institute of Applied MathematicsKhabarovsk Division54 Dzerzhinsky Street Khabarovsk 680000 Russia
2. Laboratoire Paul Painlevé LABEX‐CEMPIUniversité de LilleBatiment M2 59655 Villeneuve‐d'Ascq cedex France
3. Steklov Mathematical Institute of Russian Academy of SciencesNational Research University Higher School of Economics8 Gubkina st. Moscow 119991 Russia