Department of Computing Science, Chalmers University, SE 412 96 Göteborg, Sweden. dalevi@cs.chalmers.se|Department of Computing Science, Chalmers University, SE 412 96 Göteborg, Sweden. dalevi@cs.chalmers.se|Department of Computing Science, Chalmers University, SE 412 96 Göteborg, Sweden. dalevi@cs.chalmers.se