Syntactic complexity of ideal and closed languages

  • Authors:
  • Janusz Brzozowski;Yuli Ye

  • Affiliations:
  • David R. Cheriton School of Computer Science, University of Waterloo, Waterloo, ON, Canada;Department of Computer Science, University of Toronto, Toronto, ON, Canada

  • Venue:
  • DLT'11 Proceedings of the 15th international conference on Developments in language theory
  • Year:
  • 2011

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Abstract

The state complexity of a regular language is the number of states in the minimal deterministic automaton accepting the language. The syntactic complexity of a regular language is the cardinality of its syntactic semigroup. The syntactic complexity of a subclass of regular languages is the worst-case syntactic complexity taken as a function of the state complexity n of languages in that class. We prove that nn-1 is a tight upper bound on the complexity of right ideals and prefix-closed languages, and that there exist left ideals and suffix-closed languages of syntactic complexity nn-1 + n - 1, and two-sided ideals and factor-closed languages of syntactic complexity nn-2 + (n - 2)2n-2 + 1.