Franziska Berger Christoph Flamm Petra M. Gleiss Josef Leydold Peter F. Stadler Counterexamples in Chemical Ring Perception. 323-331 2004 44 Journal of Chemical Information and Modeling 2 http://dx.doi.org/10.1021/ci030405d db/journals/jcisd/jcisd44.html#BergerFGLS04