Oswin Aichholzer Thomas Hackl Michael Hoffmann Clemens Huemer Attila Pór Francisco Santos Bettina Speckmann Birgit Vogtenhuber http://arxiv.org/abs/0705.3820 2007 CoRR abs/0705.3820 db/journals/corr/corr0705.html#abs-0705-3820 informal publication