Affiliation: | 1. Department of Mathematical Analysis and Numerical Mathematics , Comenius University, Mlynská Dolina , 842 48, Bratislava , Slovakia;2. Mathematical Institute, Slovak Academy of Sciences , ?tefánikova 49, 814 73, Bratislava , Slovakia Michal.Feckan@fmph.uniba.sk;4. Mathematical Institute, Slovak Academy of Sciences , ?tefánikova 49, 814 73, Bratislava , Slovakia |