Unboundedness and downward closures of higher-order pushdown automata

Matthew Hague, Jonathan Kochems, C.-H. Luke Ong

Research output: Chapter in Book/Report/Conference proceedingConference contribution

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We show the diagonal problem for higher-order pushdown automata (HOPDA), and hence the simultaneous unboundedness problem, is decidable. From recent work by Zetzsche this means that we can construct the downward closure of the set of words accepted by a given HOPDA. This also means we can construct the downward closure of the Parikh image of a HOPDA. Both of these consequences play an important role in verifying concurrent higher-order programs expressed as HOPDA or safe higher-order recursion schemes.
Original languageEnglish
Title of host publicationPrinciples of Programming Languages
Subtitle of host publicationPOPL '16
Place of PublicationNew York, NY
Number of pages13
ISBN (Print)978-1-4503-3549-2
Publication statusPublished - 11 Jan 2016


  • Higher-Order Programs
  • Functional Programs
  • Model-Checking
  • Verification
  • Formal Languages
  • Downward Closures
  • Parikh Images
  • Concurrency
  • Automata
  • Pushdown Automata

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