Degrees of nondeterminism for pushdown automata

  • Kai Salomaa
  • Sheng Yu
Part of the Lecture Notes in Computer Science book series (LNCS, volume 529)


Savitch and Vermeir in [7] introduced two measures for nondeterminism of pushdown automata and showed interestingly that the second measure yields an infinite hierarchy of language families between the deterministic context-free and general context-free languages. However, the proof given in [7] for this hierarchy theorem was incorrect. In this paper, we show that all the languages used in [7] to separate different families of the hierarchy actually belong to the first level above the DCFLs. We give a new proof for the hierarchy theorem. We also introduce a new and intuitive measure for nondeterminism and show that it is equivalent to Savitch and Vermeir's second measure.


Nondeterminism pushdown automata context-free languages pumping lemmas 


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Copyright information

© Springer-Verlag Berlin Heidelberg 1991

Authors and Affiliations

  • Kai Salomaa
    • 1
  • Sheng Yu
    • 2
  1. 1.Department of MathematicsUniversity of TurkuTurkuFinland
  2. 2.Department of Computer ScienceUniversity of Western OntarioLondonCanada

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