Department of Computer and Information Science, Linköpings universitet, 581 83 Linköping, Sweden. patla@ida.liu.se|Department of Computer and Information Science, Linköpings universitet, 581 83 Linköping, Sweden. patla@ida.liu.se|Department of Computer and Information Science, Linköpings universitet, 581 83 Linköping, Sweden. patla@ida.liu.se