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Equivalence of Deterministic Top-Down Tree-to-String Transducers Is Decidable

Published: 12 April 2018 Publication History

Abstract

We prove that equivalence of deterministic top-down tree-to-string transducers is decidable, thus solving a long-standing open problem in formal language theory. We also present efficient algorithms for subclasses: for linear transducers or total transducers with unary output alphabet (over a given top-down regular domain language), as well as for transducers with the single-use restriction. These results are obtained using techniques from multi-linear algebra. For our main result, we introduce polynomial transducers and prove that for these, validity of a polynomial invariant can be certified by means of an inductive invariant of polynomial ideals. This allows us to construct two semi-algorithms, one searching for a certificate of the invariant and one searching for a witness of its violation. Via a translation into polynomial transducers, we thus obtain that equivalence of general ydt transducers is decidable. In fact, our translation also shows that equivalence is decidable when the output is not in a free monoid but in a free group.

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      cover image Journal of the ACM
      Journal of the ACM  Volume 65, Issue 4
      Distributed Computing, Cryptography, Distributed Computing, Cryptography, Coding Theory, Automata Theory, Complexity Theory, Programming Languages, Algorithms, Invited Paper Foreword and Databases
      August 2018
      307 pages
      ISSN:0004-5411
      EISSN:1557-735X
      DOI:10.1145/3208081
      Issue’s Table of Contents
      Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from [email protected]

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      Publication History

      Published: 12 April 2018
      Accepted: 01 January 2018
      Revised: 01 January 2018
      Received: 01 February 2017
      Published in JACM Volume 65, Issue 4

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      Author Tags

      1. Tree-to-string transducer
      2. decidability
      3. equivalence problem
      4. macro tree transducer
      5. polynomial ideals

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      • (2023)Deciding origin equivalence of weakly self-nesting macro tree transducersInformation Processing Letters10.1016/j.ipl.2022.106332180(106332)Online publication date: Feb-2023
      • (2023)Reverse Template Processing Using Abstract InterpretationStatic Analysis10.1007/978-3-031-44245-2_18(403-433)Online publication date: 24-Oct-2023
      • (2021)On the Balancedness of Tree-to-Word TransducersInternational Journal of Foundations of Computer Science10.1142/S012905412142007732:06(761-783)Online publication date: 14-Jul-2021
      • (2021)Streaming ranked-tree-to-string transducersTheoretical Computer Science10.1016/j.tcs.2020.12.033870(165-187)Online publication date: May-2021
      • (2020)On the Balancedness of Tree-to-Word TransducersDevelopments in Language Theory10.1007/978-3-030-48516-0_17(222-236)Online publication date: 26-May-2020
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      • (2019)Streaming Ranked-Tree-to-String TransducersImplementation and Application of Automata10.1007/978-3-030-23679-3_19(235-247)Online publication date: 26-Jun-2019
      • (2019)Deciding Equivalence of Separated Non-nested Attribute Systems in Polynomial TimeFoundations of Software Science and Computation Structures10.1007/978-3-030-17127-8_28(488-504)Online publication date: 5-Apr-2019

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