Department of Informatics, University of Oslo, PO Box 1080 Blindern, N-0316 Oslo, Norway. ole@ifi.uio.no|Department of Informatics, University of Oslo, PO Box 1080 Blindern, N-0316 Oslo, Norway. ole@ifi.uio.no|Department of Informatics, University of Oslo, PO Box 1080 Blindern, N-0316 Oslo, Norway. ole@ifi.uio.no|Department of Informatics, University of Oslo, PO Box 1080 Blindern, N-0316 Oslo, Norway. ole@ifi.uio.no|Department of Informatics, University of Oslo, PO Box 1080 Blindern, N-0316 Oslo, Norway. ole@ifi.uio.no