Abstract
Whether there exists an exponential gap between the size of a minimal deterministic two-way automaton and the size of a minimal nondeterministic two-way automaton for a specific regular language is a long standing open problem and surely one of the most challenging problems in automata theory. Twenty four years ago, Sipser [M. Sipser: Lower bounds on the size of sweeping automata. ACM STOC ’79, 360–364] showed an exponential gap between nondeterminism and determinism for the so-called sweeping automata which are automata whose head can reverse direction only at the endmarkers. Sweeping automata can be viewed as a special case of oblivious two-way automata with a number of reversals bounded by a constant.
Our first result extends the result of Sipser to general oblivious two-way automata with an unbounded number of reversals. Using this extension we show our second result, namely an exponential gap between determinism and nondeterminism for two-way automata with the degree of non-obliviousness bounded by o(n) for inputs of length n. The degree of non-obliviousness of a two-way automaton is the number of distinct orders in which the tape cells are visited.
Supported by DFG grants HR 1416-1 and SCHN 50312-1.
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Hromkovič, J., Schnitger, G. (2003). Nondeterminism versus Determinism for Two-Way Finite Automata: Generalizations of Sipser’s Separation. In: Baeten, J.C.M., Lenstra, J.K., Parrow, J., Woeginger, G.J. (eds) Automata, Languages and Programming. ICALP 2003. Lecture Notes in Computer Science, vol 2719. Springer, Berlin, Heidelberg. https://doi.org/10.1007/3-540-45061-0_36
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DOI: https://doi.org/10.1007/3-540-45061-0_36
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