Decision Problems for Semi-Thue Systems with a Few Rules

  • Authors:
  • Yuri Matiyasevich;Geraud Senizergues

  • Affiliations:
  • -;-

  • Venue:
  • LICS '96 Proceedings of the 11th Annual IEEE Symposium on Logic in Computer Science
  • Year:
  • 1996

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Abstract

For several decision problems about semi-Thue systems , we try to locate the frontier between the decidable and the undecidable from the point of view of the number of rules. We show that the the Termination Problem, the U-Termination Problem, the Accessibility Problem and the Common-Descendant Problem are undecidable for 3 rules semi-Thue systems . As a corollary we obtain the undecidability of the Post-Correspondence Problem for 7 pairs of words.