Institution: | Institute für Angewandte Mathematik, Univ. Bonn, Wegelerstr. 6, 53155 Bonn, Germany; SFB 256 Bonn, BiBoS, Bielefeld-Bonn, CERFIM, Locarno and USI (Switzerland) ; Institute of Mathematics, vul. Tereschenkivs'ka, 3, Kyiv, 01601 Ukraine ; Department of Mathematics, Stockholm University, 106 91 Stockholm, Sweden ; Institute of Mathematics, vul. Tereschenkivs'ka, 3, Kyiv, 01601 Ukraine |