1. CEG-IST; Instituto Superior Técnico, Technical University of Lisbon; Av. Rovisco Pais 1049-001 Lisboa Portugal
2. Department of Economics and Business; University of Catania; Corso Italia, 55 95 129 Catania Italy
3. LAMSADE; Université Paris-Dauphine; Place du Maréchal De Lattre de Tassigny F-75 775 Paris Cedex 16 France
4. Institute of Computing Science; Poznań University of Technology; 60-965 Poznań Poland
5. Systems Research Institute; Polish Academy of Sciences; 01-447 Warsaw Poland