Playing with Conway's problem

  • Authors:
  • Emmanuel Jeandel;Nicolas Ollinger

  • Affiliations:
  • LIP, École Normale Supérieure de Lyon, CNRS, 46 allée dItalie, 69007 Lyon, France and LIF, Aix-Marseille Université, CNRS, 39 rue Joliot-Curie, 13013 Marseille, France;LIF, Aix-Marseille Université, CNRS, 39 rue Joliot-Curie, 13013 Marseille, France

  • Venue:
  • Theoretical Computer Science
  • Year:
  • 2008

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Abstract

The centralizer of a language is the maximal language commuting with it. The question, raised by Conway in [J.H. Conway, Regular Algebra and Finite Machines, Chapman Hall, 1971], whether the centralizer of a rational language is always rational, recently received a lot of attention. In Kunc [M. Kunc, The power of commuting with finite sets of words, in: Proc. of STACS 2005, in: LNCS, vol. 3404, Springer, 2005, pp. 569-580], a strong negative answer to this problem was given by showing that even complete co-recursively enumerable centralizers exist for finite languages. Using a combinatorial game approach, we give here an incremental construction of rational languages embedding any recursive computation in their centralizers.