1. Faculty of Information Technology, University of Jyväskylä, P.O. Box 35 (Ag C416.2), FI-40014 University of Jyväskylä, Jyväskylä, Finland. antti.valmari@jyu.fi
2. Institut für Informatik, University of Augsburg, D-86135 Augsburg, Germany. walter.vogler@informatik.uni-augsburg.de