Alexander Ullrich Christoph Flamm Functional Evolution of Ribozyme-Catalyzed Metabolisms in a Graph-Based Toy-Universe. 28-43 2008 CMSB http://dx.doi.org/10.1007/978-3-540-88562-7_7 conf/cmsb/2008 db/conf/cmsb/cmsb2008.html#UllrichF08