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Cancellation in context-free languages: Enrichment by reduction

  • M. Jantzen
  • H. Petersen
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 665)

Abstract

The following problem is shown to be decidable: Given a context-free grammar G and a string w ∈ X*, does there exist a string u ∈ L(G) such that w is obtained from u by deleting all substrings u i , that are elements of the symmetric Dyck set D 1 * ?

The intersection of any two context-free languages can be obtained from only one context-free language by cancellation either with the smaller semi-Dyck set D 1 ′* D 1 * or with D 1 * itself.

Also, the following is shown here for the first time: If the set EQ ≔ {xn¯xn¦ n ∈ND 1 ′* is used for this cancellation, then each recursively enumerable set can be obtained from linear context-free languages.

Keywords

Sentential Form Terminal Symbol Formal Language Theory Nonterminal Symbol Counter Automaton 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag Berlin Heidelberg 1993

Authors and Affiliations

  • M. Jantzen
    • 1
  • H. Petersen
    • 1
  1. 1.Fachbereich InformatikUniversität HamburgGermany

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