Karsten Klein Nils Kriege Petra Mutzel CT-index: Fingerprint-based graph indexing combining cycles and trees. 1115-1126 2011 ICDE http://doi.ieeecomputersociety.org/10.1109/ICDE.2011.5767909 conf/icde/2011 db/conf/icde/icde2011.html#KleinKM11