Jurek Czyzowicz Stefan Dobrev Evangelos Kranakis Danny Krizanc The Power of Tokens: Rendezvous and Symmetry Detection for Two Mobile Agents in a Ring. 234-246 2008 conf/sofsem/2008 SOFSEM http://dx.doi.org/10.1007/978-3-540-77566-9_20 db/conf/sofsem/sofsem2008.html#CzyzowiczDKK08