Advances in artificial intelligence (vol. # 3955) : 4th Helenic Conference on AI, SETN 2006, Heraklion, Crete, Greece, May 18-20, 2006, Proceedings - Antoniou, Grigoris; Potamias, George; Spyropoulos, Costas; Plexousakis, Dimitris (Lecture Notes in Computer Science,, 2006)