Comparing consecutive letter counts in multiple context-free languages

Florian Lehner*, Christian Lindorfer

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Context-free grammars are not able to capture cross-serial dependencies occurring in some natural languages. To overcome this issue, Seki et al. introduced a generalization called m-multiple context-free grammars (m-MCFGs), which deal with m-tuples of strings. We show that m-MCFGs are capable of comparing the number of consecutive occurrences of at most 2m different letters. In particular, the language {a 1 n 1 a 2 n 2 ⋯a 2m+1 n 2m+1 |n 1≥n 2≥…≥n 2m+1≥0} is (m+1)-multiple context-free, but not m-multiple context-free.

Original languageEnglish
Pages (from-to)1-5
Number of pages5
JournalTheoretical Computer Science
Publication statusPublished - 8 May 2021


  • Formal language
  • Multiple context free language

ASJC Scopus subject areas

  • Theoretical Computer Science
  • Computer Science(all)


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