Note: on ground tree transformations and congruences induced by tree automata

  • Authors:
  • Sándor Vágvölgyi

  • Affiliations:
  • Department of Applied Informatics University of Szeged Árpád tér 2, H-6720 Szeged, Hungary

  • Venue:
  • Theoretical Computer Science
  • Year:
  • 2003

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Abstract

For a tree automaton A over a ranked alphabet Σ, we study the ground tree transformation π(A) induced by A and the restriction θ(A) of the congruence ↔A* to terms over Σ. We define a congruence relation ρ ⊆ A × A on A, called the determiner of A, and the quotient tree automaton A/ρ. We show the following results. It is decidable if θ(A) = π(A). If A is deterministic, then θ(A) = π(A). The determiner ρ of A can be effectively constructed, A/ρ is deterministic, and θ(A) = θ(A/ρ). For a connected tree automaton A, π(A) = π(A/ρ) if and only if π(A) = π(B) for some deterministic tree automaton B if and only if θ(A) = π(A).