1. National Institute of Information and Communications Technology (NICT), Center for Information and Neural Networks (CiNet), Osaka, Japan. matthew@nict.go.jp
2. Department of Mathematics, TU Darmstadt, Darmstadt, Germany. matthias.schroeder@cca-net.de
3. A.P. Ershov Institute of Informatics Systems SB RAS, Novosibirsk, Russia. vseliv@iis.nsk.su