Greg Aloupis Jean Cardinal Sébastien Collette S. Imahori M. Korman Stefan Langerman O. Schwartz Shakhar Smorodinsky Perouz Taslakian http://arxiv.org/abs/0904.2115 2009 CoRR abs/0904.2115 db/journals/corr/corr0904.html#abs-0904-2115 informal publication