Abstract
A non-deterministic automaton on infinite trees is unambiguous if it has at most one accepting run on every tree. For a given unambiguous parity automaton \(\mathcal {A} \) of index (i, 2j) we construct an alternating automaton \(\textsc {Transformation}(\mathcal {A})\) which accepts the same language, but is simpler in terms of alternating hierarchy of automata. If \(\mathcal {A} \) is a Büchi automaton (\(i=0, j=1\)), then \(\textsc {Transformation}(\mathcal {A})\) is a weak alternating automaton. In general, \(\textsc {Transformation}(\mathcal {A})\) belongs to the class \(\mathrm {Comp}({i}+1,2{j})\), in particular it is simultaneously of alternating index (i, 2j) and of the dual index \((i+1,2j+1)\). The main theorem of this paper is a correctness proof of the algorithm \(\textsc {Transformation}\). The transformation algorithm is based on a separation algorithm of Arnold and Santocanale (2005) and extends results of Finkel and Simonnet (2009).
The authors were supported by the Polish National Science Centre grant no. 2014-13/B/ST6/03595.
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Notes
- 1.
By Lemma 4 there is at most one such \(\delta \).
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Michalewski, H., Skrzypczak, M. (2016). Unambiguous Büchi Is Weak. In: Brlek, S., Reutenauer, C. (eds) Developments in Language Theory. DLT 2016. Lecture Notes in Computer Science(), vol 9840. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-662-53132-7_26
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