Greg Aloupis Sébastien Collette Erik D. Demaine Stefan Langerman Vera Sacristan Stefanie Wuhrer Reconfiguration of 3D Crystalline Robots Using O(log n) Parallel Moves http://arxiv.org/abs/0908.2440 2009 CoRR abs/0908.2440 db/journals/corr/corr0908.html#abs-0908-2440 informal publication