======================================= Artur Kornilowicz e-mail: arturk@math.uwb.edu.pl Dept. of Applied Logic http://math.uwb.edu.pl/~arturk/ Institute of Computer Science fax. +48 (85) 745-7073 University of Bialystok tel. +48 (85) 745-7559 (office) 15-267 Bialystok, Poland +48 (85) 651-6193 (home)