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Reachability in Pushdown Register Automata

Research output: Contribution to journalArticle

Original languageEnglish
Pages (from-to)58-83
Number of pages26
JournalJournal of Computer and System Sciences
Early online date8 Mar 2017
DateAccepted/In press - 13 Feb 2017
DateE-pub ahead of print - 8 Mar 2017
DatePublished (current) - Aug 2017


We investigate reachability in pushdown automata over infinite alphabets. We show that, in terms of reachability/emptiness, these machines can be faithfully represented using only 3r elements of the alphabet, where r is the number of registers. We settle the complexity of associated reachability/emptiness problems. In contrast to register automata, the emptiness problem for pushdown register automata is EXPTIME-complete, independent of the register storage policy used. We also solve the global reachability problem by representing pushdown configurations with a special register automaton. Finally, we examine extensions of pushdown storage to higher orders and show that reachability is undecidable at order 2.

    Research areas

  • Register automata, Pushdown automata, Reachability, Infinite alphabets, Complexity

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    Licence: CC BY


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