Recognizing boolean closed A-tree languages with membership conditional rewriting mechanism

  • Authors:
  • Hitoshi Ohsaki;Hiroyuki Seki;Toshinori Takai

  • Affiliations:
  • PRESTO “Information and Systems” Japan Science and Technology Corporation and National Institute of Advanced Industrial Science and Technology, Amagasaki, Japan;Nara Institute of Science and Technology, Ikoma, Japan;National Institute of Advanced Industrial Science and Technology, Amagasaki, Japan

  • Venue:
  • RTA'03 Proceedings of the 14th international conference on Rewriting techniques and applications
  • Year:
  • 2003

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Abstract

This paper provides an algorithm to compute the complement of tree languages recognizable with A-TA (tree automata with associativity axioms [16]). Due to this closure property together with the previously obtained results, we know that the class is boolean closed, while keeping recognizability of A-closures of regular tree languages. In the proof of the main result, a new framework of tree automata, called sequence-tree automata, is introduced as a generalization of Lugiez and Dal Zilio's multi-tree automata [14] of an associativity case. It is also shown that recognizable A-tree languages are closed under a one-step rewrite relation in case of ground A-term rewriting. This result allows us to compute an under-approximation of A-rewrite descendants of recognizable A-tree languages with arbitrary accuracy.