Hans-Jörg Kreowski Renate Klempien-Hinrichs Sabine Kuske Some Essentials of Graph Transformation. 229-254 2006 Recent Advances in Formal Languages and Applications http://dx.doi.org/10.1007/978-3-540-33461-3_9 series/sci/2006-25 db/series/sci/sci25.html#KreowskiKK06