## Abstract

It is shown that for every constant m it can be decided in polynomial time whether or not two m-ambiguous finite tree automata are equivalent. In general, inequivalence for finite tree automata is DEXPTIME-complete with respect to logspace reductions, and PSPACE-complete with respect to logspace reductions, if the automata in question are supposed to accept only finite languages. For finite tree automata with weights in a field R, a polynomial time algorithm is presented for deciding ambiguity-equivalence, provided R-operations and R-tests for 0 can be performed in constant time. This result is used to construct an algorithm deciding ambiguity-inequivalence of finite tree automata in randomized polynomial time. Finally, for every constant m it is shown that it can be decided in polynomial time whether or not a given finite tree automation is m-ambiguous.

Original language | English |
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Pages (from-to) | 424-437 |

Number of pages | 14 |

Journal | SIAM Journal on Computing |

Volume | 19 |

Issue number | 3 |

DOIs | |

State | Published - 1990 |

Externally published | Yes |