On Stateless Multihead Automata: Hierarchies and the Emptiness Problem

  • Oscar H. Ibarra
  • Juhani Karhumäki
  • Alexander Okhotin
Part of the Lecture Notes in Computer Science book series (LNCS, volume 4957)


We look at stateless multihead finite automata in their two-way and one-way, deterministic and nondeterministic variations. The transition of a k-head automaton depends solely on the symbols currently scanned by its k heads, and every such transition moves each head one cell left or right, or instructs it to stay. We show that stateless (k + 4)-head two-way automata are more powerful than stateless k-head two-way automata. In the one-way case, we prove a tighter result: stateless (k + 1)-head one-way automata are more powerful than stateless k-head one-way automata. Finally, we show that the emptiness problem for stateless 2-head two-way automata is undecidable.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2008

Authors and Affiliations

  • Oscar H. Ibarra
    • 1
  • Juhani Karhumäki
    • 2
  • Alexander Okhotin
    • 2
    • 3
  1. 1.Department of Computer ScienceUniversity of CaliforniaSanta BarbaraUSA
  2. 2.Department of MathematicsUniversity of TurkuTurkuFinland
  3. 3.Academy of Finland 

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