1. Department of Mathematical Analysis and Numerical Mathematics, Faculty of Mathematics, Physics and Informatics, Comenius University 2 in Bratislava, Mlynská dolina, 842 48 Bratislava, Slovakia and , Štefánikova 49, 814 73 Bratislava, Slovakia
2. Mathematical Institute, Slovak Academy of Sciences 2 in Bratislava, Mlynská dolina, 842 48 Bratislava, Slovakia and , Štefánikova 49, 814 73 Bratislava, Slovakia