On the Density of Context-Free and Counter Languages

  • Joey Eremondi
  • Oscar H. Ibarra
  • Ian McQuillanEmail author
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 9168)


A language L is said to be dense if every word in the universe is an infix of some word in L. This notion has been generalized from the infix operation to arbitrary word operations \(\varrho \) in place of the infix operation (\(\varrho \)-dense, with infix-dense being the standard notion of dense). It is shown here that it is decidable, for a language L accepted by a one-way nondeterministic reversal-bounded pushdown automaton, whether L is infix-dense. However, it becomes undecidable for both deterministic pushdown automata (with no reversal-bound), and for nondeterministic one-counter automata. When examining suffix-density, it is undecidable for more restricted families such as deterministic one-counter automata that make three reversals on the counter, but it is decidable with less reversals. Other decidability results are also presented on dense languages, and contrasted with a marked version called \(\varrho \)-marked-density. Also, new languages are demonstrated to be outside various deterministic language families after applying different deletion operations from smaller families. Lastly, bounded-dense languages are defined and examined.


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Copyright information

© Springer International Publishing Switzerland 2015

Authors and Affiliations

  • Joey Eremondi
    • 1
  • Oscar H. Ibarra
    • 2
  • Ian McQuillan
    • 3
    Email author
  1. 1.Department of Information and Computing SciencesUtrecht UniversityUtrechtThe Netherlands
  2. 2.Department of Computer ScienceUniversity of CaliforniaSanta BarbaraUSA
  3. 3.Department of Computer ScienceUniversity of SaskatchewanSaskatoonCanada

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