Helsinki Institute for Information Technology HIIT, Department of Computer Science, University of Helsinki, Finland. tomescu@cs.helsinki.fi.|Helsinki Institute for Information Technology HIIT, Department of Computer Science, University of Helsinki, Finland. tomescu@cs.helsinki.fi.|Helsinki Institute for Information Technology HIIT, Department of Computer Science, University of Helsinki, Finland. tomescu@cs.helsinki.fi.|Helsinki Institute for Information Technology HIIT, Department of Computer Science, University of Helsinki, Finland. tomescu@cs.helsinki.fi.