Institution: | (1) Department of Mechanics and Mathematics, Ivan Franko Lviv National University, Universytetska 1, Lviv, 79000, Ukraine;(2) Department of Mathematics, Louisiana State University, Baton Rouge, LA 70803, USA;(3) Institute of Mathematics, Physics and Mechanics, Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, Ljubljana, 1000, Slovenia |