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DOI: 10.4230/LIPIcs.MFCS.2020.69

Regular Choice Functions and Uniformisations For countable Domains

Authors: Vincent Michielini and Michał Skrzypczak

Published in: LIPIcs, Volume 170, 45th International Symposium on Mathematical Foundations of Computer Science (MFCS 2020)

Abstract

We view languages of words over a product alphabet A x B as relations between words over A and words over B. This leads to the notion of regular relations - relations given by a regular language. We ask when it is possible to find regular uniformisations of regular relations. The answer depends on the structure or shape of the underlying model: it is true e.g. for ω-words, while false for words over ℤ or for infinite trees. In this paper we focus on countable orders. Our main result characterises, which countable linear orders D have the property that every regular relation between words over D has a regular uniformisation. As it turns out, the only obstacle for uniformisability is the one displayed in the case of ℤ - non-trivial automorphisms of the given structure. Thus, we show that either all regular relations over D have regular uniformisations, or there is a non-trivial automorphism of D and even the simple relation of choice cannot be uniformised. Moreover, this dichotomy is effective.

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Vincent Michielini and Michał Skrzypczak. Regular Choice Functions and Uniformisations For countable Domains. In 45th International Symposium on Mathematical Foundations of Computer Science (MFCS 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 170, pp. 69:1-69:13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{michielini_et_al:LIPIcs.MFCS.2020.69,
  author =	{Michielini, Vincent and Skrzypczak, Micha{\l}},
  title =	{{Regular Choice Functions and Uniformisations For countable Domains}},
  booktitle =	{45th International Symposium on Mathematical Foundations of Computer Science (MFCS 2020)},
  pages =	{69:1--69:13},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-159-7},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{170},
  editor =	{Esparza, Javier and Kr\'{a}l', Daniel},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2020.69},
  URN =		{urn:nbn:de:0030-drops-127386},
  doi =		{10.4230/LIPIcs.MFCS.2020.69},
  annote =	{Keywords: Uniformisation, Monadic Second-order logic, Countable words}
}

Document

DOI: 10.4230/LIPIcs.MFCS.2019.61

Uniformisation Gives the Full Strength of Regular Languages

Authors: Nathan Lhote, Vincent Michielini, and Michał Skrzypczak

Published in: LIPIcs, Volume 138, 44th International Symposium on Mathematical Foundations of Computer Science (MFCS 2019)

Abstract

Given R a binary relation between words (which we treat as a language over a product alphabet AxB), a uniformisation of it is another relation L included in R which chooses a single word over B, for each word over A whenever there exists one. It is known that MSO, the full class of regular languages, is strong enough to define a uniformisation for each of its relations. The quest of this work is to see which other formalisms, weaker than MSO, also have this property. In this paper, we solve this problem for pseudo-varieties of semigroups: we show that no nonempty pseudo-variety weaker than MSO can provide uniformisations for its relations.

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Nathan Lhote, Vincent Michielini, and Michał Skrzypczak. Uniformisation Gives the Full Strength of Regular Languages. In 44th International Symposium on Mathematical Foundations of Computer Science (MFCS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 138, pp. 61:1-61:13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{lhote_et_al:LIPIcs.MFCS.2019.61,
  author =	{Lhote, Nathan and Michielini, Vincent and Skrzypczak, Micha{\l}},
  title =	{{Uniformisation Gives the Full Strength of Regular Languages}},
  booktitle =	{44th International Symposium on Mathematical Foundations of Computer Science (MFCS 2019)},
  pages =	{61:1--61:13},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-117-7},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{138},
  editor =	{Rossmanith, Peter and Heggernes, Pinar and Katoen, Joost-Pieter},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2019.61},
  URN =		{urn:nbn:de:0030-drops-110053},
  doi =		{10.4230/LIPIcs.MFCS.2019.61},
  annote =	{Keywords: pseudo-variety, finite word, semigroup, uniformisation, regular language}
}

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Regular Choice Functions and Uniformisations For countable Domains

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Uniformisation Gives the Full Strength of Regular Languages

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