1. J. Balcázar, J. Díaz and J. Gabarró, Structural Complexity I and II, (Springer-Verlag, 1990).
2. L. Cai, The computational complexity of PCGS with regular components. Proceedings 2nd International Conference on Development in Language Theory, World Sci. Publ., Singapore, 1996, 209–219.
3. L. Cai, The complexity of linear PCGSs, Computers and Artificial Intelligence, 15, 2–3 (1996), pp. 199–210.
4. S. Cook, A Taxonomy of problems with fast parallel algorithms, Information and Control, 64 (1985), 2–22.
5. E. Csuhaj-Varjú, J. Dassow, J. Kelemen, and Gh. Păun, Grammar Systems, (Gordon and Breach Sci. Publishers Ltd., 1993).