1. Faculty of Mechanics and Mathematics, Novosibirsk State University, Novosibirsk, Russia
2. Institute of Informatics Systems, Siberian Division of the Russian Academy of Sciences, Novosibirsk, Russia. bozhenko@iis.nsk.su
3. Institute of Informatics Systems, Siberian Division of the Russian Academy of Sciences, Novosibirsk, Russia. virb@iis.nsk.su