1 Dept. of Mathematics and Statistics, Southern Illinois University Edwardsville, Edwardsville, Illinois, 62026-1653
2 Institute of Mathematics, Technical University of Lodz, Wolczanska 215, 90-924 Lodz
3 University of Lodz, Faculty of Math & Computer Sciences, Banacha 22, 90-238 Lodz
4 Department of Automatic Control, Silesian University of Technology, 44-101 Gliwice
5 Institute of Mathematics, Warsaw University, ul. Banacha 2, 02-097 W-wa
6 University of Bialystok, ul. Akademicka 2, 15-267 Białystok