Abstract
We show that, in the case of context-free programmed grammars with appearance checking working under free derivations, three nonterminals are enough to generate every recursively enumerable language. This improves the previously published bound of eight for the nonterminal complexity of these grammars. This also yields an improved nonterminal complexity bound of four for context-free matrix grammars with appearance checking. Moreover, we establish nonterminal complexity bounds for context-free programmed and matrix grammars working under leftmost derivations.
Acknowledgments
We are grateful for immediate answers of our colleagues H.Bordihn and Gh.Păun concerning questions on syntactic complexity and for some discussions with R.F reund and F.Stephan.
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Fernau, H. (2001). Nonterminal Complexity of Programmed Grammars. In: Margenstern, M., Rogozhin, Y. (eds) Machines, Computations, and Universality. MCU 2001. Lecture Notes in Computer Science, vol 2055. Springer, Berlin, Heidelberg. https://doi.org/10.1007/3-540-45132-3_13
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DOI: https://doi.org/10.1007/3-540-45132-3_13
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