Affiliation: | 1. Department of Mathematical Analysis, Charles University, Sokolovská 83, 186 00 Prague 8, Czech Republic;2. Department of Mathematics and Statistics, P.O. Box 35, FIN-40014, University of Jyväskylä, Finland;3. Department of Technology, Jyväskylä University of Applied Sciences, P.O. Box 207, FIN-40101 Jyväskylä, Finland |