no. R1
Bicolored digraph grammar systems
Revue française d'automatique informatique recherche opérationnelle. Mathématique, Tome 7 (1973) no. R1, pp. 45-52 
@article{M2AN_1973__7_1_45_0,
     author = {Wood, Derick},
     title = {Bicolored digraph grammar systems},
     journal = {Revue fran\c{c}aise d'automatique informatique recherche op\'erationnelle. Math\'ematique},
     pages = {45--52},
     year = {1973},
     publisher = {Dunod},
     address = {Paris},
     volume = {7},
     number = {R1},
     mrnumber = {388874},
     zbl = {0262.68014},
     language = {en},
     url = {https://www.numdam.org/item/M2AN_1973__7_1_45_0/}
}
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Wood, Derick. Bicolored digraph grammar systems. Revue française d'automatique informatique recherche opérationnelle. Mathématique, Tome 7 (1973) no. R1, pp. 45-52. https://www.numdam.org/item/M2AN_1973__7_1_45_0/

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Harary F., Norman R. Z., and Cartwright D., Structural models, 1965, JohnWiley andSon. | Zbl

Rosenkrantz D. J., Programmed grammars and classes offormal languages, JACM 16 1969, 1, pp. 107-131. | Zbl | MR

Salomaa A., Formal languages, to be published by Academic Press, 1973. | Zbl | MR