1. Department of Computer Science, Aalto University, Finland. E-mails: kasper.apajalahti@aalto.fi, eero.hyvonen@aalto.fi
2. Department of Mathematics and Statistics, University of Helsinki, Finland. E-mail: juha.niiranen@helsinki.fi
3. Nokia Bell Labs, Finland. E-mail: vilho.raisanen@nokia-bell-labs.com