1. J. Adamek, H. Herrlich, and G. Strecker: 1990,Abstract and Concrete Categories, Wiley Interscience.
2. M. Beyer, H. Ehrig, and M. L�we (eds.): 1992,Computing by Graph Transformation (COMPUGRAPH) ? Survey, Results, and Application, Booklet for the presentation of ESPRIT BR WG No. 3299 at CeBIT fair, Hannover.
3. P. Boehm, H. Fonio, and A. Habel: 1987, ?Amalgamation of graph transformations: A synchronization mechanism?,JCSS 34, 307?408.
4. P.M. van den Broek: 1991,Algebraic Graph Rewriting Using a Single Pushout, International Joint Conf. on Theory and Practice of Software Development 1991 (TAPSOFT'91), LNCS 493, pp. 90?102.
5. A. Corradini, H. Ehrig, M. L�we, U. Montanari, and F. Rossi: 1992, ?Note on Standard Representation of Graphs and Graph Derivations?, Technical Report TU Berlin, FB 20, No. 92?25.