1. Fu, K.S.: Syntactic Methods in Pattern Recognition, Academic Press New York 1974
2. Gonzalez, R.C.; Thomason, M.G.: Syntactic Pattern Recognition, Addison-Wesley Reading 1978
3. Pavlidis, T.: Linear and Context-Free Graph Grammars, Journal of the ACM 19 (1972), 193–220
4. Della Vigna, P.; Ghezzi, C.: Context-Free Graph Grammars, Information and Control 37 (1978), 207–233
5. Nagl, M.: Formal Languages of Labelled Graphs, Computing 16 (1976), 113–137