1. IST Austria (Institute of Science and Technology Austria), Klosterneuburg, 3400, Austria.
2. School of Mathematical and Statistical Sciences, University of Texas Rio Grande Valley, Brownsville, TX 78520 USA.
3. Khoury College of Computer Sciences, Northeastern University, Boston, MA 02115 USA.
4. Inria centre Université Côte d’Azur, France.