Department of Computer Science, Technion-Israel Institute of Technology, Haifa 32000, Israel. pinter@cs.technion.ac.il|Department of Computer Science, Technion-Israel Institute of Technology, Haifa 32000, Israel. pinter@cs.technion.ac.il|Department of Computer Science, Technion-Israel Institute of Technology, Haifa 32000, Israel. pinter@cs.technion.ac.il|Department of Computer Science, Technion-Israel Institute of Technology, Haifa 32000, Israel. pinter@cs.technion.ac.il