Remarks on the nonexistence of some covering grammars

  • Esko Ukkonen
Vorträge (In Alphabetischer Reihenfolge)
Part of the Lecture Notes in Computer Science book series (LNCS, volume 67)


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.


Normal Form Derivation Tree Empty String Start Symbol Recursive Part 


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© Springer-Verlag Berlin Heidelberg 1979

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  • Esko Ukkonen

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