1. Information and Communication Technologies, National Research Council Canada, Moncton, N.B. E1A 7R1, Canada
2. Dalle Molle Institute for Artificial Intelligence (IDSIA), University of Applied Sciences of Southern Switzerland (SUPSI), Galleria 2, CH-6928 Manno, Switzerland
3. Division of Mathematics and Statistics, University of South Wales, Pontypridd, CF37 1DL, United Kingdom