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Documents authored by Urabe, Natsuki

Document
Early Ideas
DOI: 10.4230/LIPIcs.CALCO.2021.21
Preorder-Constrained Simulation for Nondeterministic Automata (Early Ideas)

Authors: Koko Muroya, Takahiro Sanada, and Natsuki Urabe

Published in: LIPIcs, Volume 211, 9th Conference on Algebra and Coalgebra in Computer Science (CALCO 2021)

Abstract
We describe our ongoing work on generalizing some quantitatively constrained notions of weak simulation up-to that are recently introduced for deterministic systems modeling program execution. We present and discuss a new notion dubbed preorder-constrained simulation that allows comparison between words using a preorder, instead of equality.
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Koko Muroya, Takahiro Sanada, and Natsuki Urabe. Preorder-Constrained Simulation for Nondeterministic Automata (Early Ideas). In 9th Conference on Algebra and Coalgebra in Computer Science (CALCO 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 211, pp. 21:1-21:5, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{muroya_et_al:LIPIcs.CALCO.2021.21,
  author =	{Muroya, Koko and Sanada, Takahiro and Urabe, Natsuki},
  title =	{{Preorder-Constrained Simulation for Nondeterministic Automata}},
  booktitle =	{9th Conference on Algebra and Coalgebra in Computer Science (CALCO 2021)},
  pages =	{21:1--21:5},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-212-9},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{211},
  editor =	{Gadducci, Fabio and Silva, Alexandra},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CALCO.2021.21},
  URN =		{urn:nbn:de:0030-drops-153762},
  doi =		{10.4230/LIPIcs.CALCO.2021.21},
  annote =	{Keywords: simulation, weak simulation, up-to technique, language inclusion, preorder}
}
Document
DOI: 10.4230/LIPIcs.CONCUR.2016.24
Coalgebraic Trace Semantics for Buechi and Parity Automata

Authors: Natsuki Urabe, Shunsuke Shimizu, and Ichiro Hasuo

Published in: LIPIcs, Volume 59, 27th International Conference on Concurrency Theory (CONCUR 2016)

Abstract
Despite its success in producing numerous general results on state-based dynamics, the theory of coalgebra has struggled to accommodate the Buechi acceptance condition---a basic notion in the theory of automata for infinite words or trees. In this paper we present a clean answer to the question that builds on the "maximality" characterization of infinite traces (by Jacobs and Cirstea): the accepted language of a Buechi automaton is characterized by two commuting diagrams, one for a least homomorphism and the other for a greatest, much like in a system of (least and greatest) fixed-point equations. This characterization works uniformly for the nondeterministic branching and the probabilistic one; and for words and trees alike. We present our results in terms of the parity acceptance condition that generalizes Buechi's.
Cite as

Natsuki Urabe, Shunsuke Shimizu, and Ichiro Hasuo. Coalgebraic Trace Semantics for Buechi and Parity Automata. In 27th International Conference on Concurrency Theory (CONCUR 2016). Leibniz International Proceedings in Informatics (LIPIcs), Volume 59, pp. 24:1-24:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2016)

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@InProceedings{urabe_et_al:LIPIcs.CONCUR.2016.24,
  author =	{Urabe, Natsuki and Shimizu, Shunsuke and Hasuo, Ichiro},
  title =	{{Coalgebraic Trace Semantics for Buechi and Parity Automata}},
  booktitle =	{27th International Conference on Concurrency Theory (CONCUR 2016)},
  pages =	{24:1--24:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-017-0},
  ISSN =	{1868-8969},
  year =	{2016},
  volume =	{59},
  editor =	{Desharnais, Jos\'{e}e and Jagadeesan, Radha},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2016.24},
  URN =		{urn:nbn:de:0030-drops-61867},
  doi =		{10.4230/LIPIcs.CONCUR.2016.24},
  annote =	{Keywords: coalgebra, Buechi automaton, parity automaton, probabilistic automaton, tree automaton}
}
Document
DOI: 10.4230/LIPIcs.CALCO.2015.320
Coalgebraic Infinite Traces and Kleisli Simulations

Authors: Natsuki Urabe and Ichiro Hasuo

Published in: LIPIcs, Volume 35, 6th Conference on Algebra and Coalgebra in Computer Science (CALCO 2015)

Abstract
Kleisli simulation is a categorical notion introduced by Hasuo to verify finite trace inclusion. They allow us to give definitions of forward and backward simulation for various types of systems. A generic categorical theory behind Kleisli simulation has been developed and it guarantees the soundness of those simulations wrt. finite trace semantics. Moreover, those simulations can be aided by forward partial execution (FPE) - a categorical transformation of systems previously introduced by the authors. In this paper, we give Kleisli simulation a theoretical foundation that assures its soundness also wrt. infinite trace. There, following Jacobs' work, infinite trace semantics is characterized as the "largest homomorphism." It turns out that soundness of forward simulations is rather straightforward; that of backward simulation holds too, although it requires certain additional conditions and its proof is more involved. We also show that FPE can be successfully employed in the infinite trace setting to enhance the applicability of Kleisli simulations as witnesses of trace inclusion. Our framework is parameterized in the monad for branching as well as in the functor for linear-time behaviors; for the former we use the powerset monad (for nondeterminism) as well as the sub-Giry monad (for probability).
Cite as

Natsuki Urabe and Ichiro Hasuo. Coalgebraic Infinite Traces and Kleisli Simulations. In 6th Conference on Algebra and Coalgebra in Computer Science (CALCO 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 35, pp. 320-335, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2015)

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@InProceedings{urabe_et_al:LIPIcs.CALCO.2015.320,
  author =	{Urabe, Natsuki and Hasuo, Ichiro},
  title =	{{Coalgebraic Infinite Traces and Kleisli Simulations}},
  booktitle =	{6th Conference on Algebra and Coalgebra in Computer Science (CALCO 2015)},
  pages =	{320--335},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-84-2},
  ISSN =	{1868-8969},
  year =	{2015},
  volume =	{35},
  editor =	{Moss, Lawrence S. and Sobocinski, Pawel},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CALCO.2015.320},
  URN =		{urn:nbn:de:0030-drops-55424},
  doi =		{10.4230/LIPIcs.CALCO.2015.320},
  annote =	{Keywords: category theory, coalgebra, simulation, verification, trace semantics}
}
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