Abstract
The problem of covering context-free grammars by grammars in some normal forms is considered. It is shown that certain example grammars cannot be covered by grammars which are in ε-free form or in Greibach normal form or in Chomsky normal form. The results are generalized using a concept called the structural similarity of context-free grammars. Finally, a grammatical transformation method for constructing ε-free covers is given.
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Ukkonen, E. (1979). Remarks on the nonexistence of some covering grammars. In: Weihrauch, K. (eds) Theoretical Computer Science 4th GI Conference. Lecture Notes in Computer Science, vol 67. Springer, Berlin, Heidelberg. https://doi.org/10.1007/3-540-09118-1_31
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DOI: https://doi.org/10.1007/3-540-09118-1_31
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