Note: On the complexity of computing the profinite closure of a rational language

  • Authors:
  • P. -C. Héam

  • Affiliations:
  • -

  • Venue:
  • Theoretical Computer Science
  • Year:
  • 2011

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Abstract

Profinite topology is used in the classification of rational languages. In particular, several important decidability problems, related to the Malcev product, reduce to the computation of the closure of a rational language in the profinite topology. It is known that, given a rational language by a deterministic automaton, computing a deterministic automaton accepting its profinite closure can be done with an exponential upper bound. This paper is dedicated the study of a lower bound for this problem: we prove that, in some cases, if the alphabet contains at least three letters, it requires an exponential time.