3 Search Results for "Ciobanu, Laura"

Document
DOI: 10.4230/LIPIcs.STACS.2026.77
An Improved Version of Hmelevskii’s Theorem on Three-Variable Word Equations

Authors: Aleksi Saarela

Published in: LIPIcs, Volume 364, 43rd International Symposium on Theoretical Aspects of Computer Science (STACS 2026)

Abstract
Hmelevskii proved in 1971 that every constant-free three-variable word equation has a parametric solution. We prove an improved version of this result by showing that every such equation has a parametric solution using only three numerical parameters and with only two levels of nesting. This means that the structure of the solution sets of these equations is considerably simpler than has been known before.
Cite as

Aleksi Saarela. An Improved Version of Hmelevskii’s Theorem on Three-Variable Word Equations. In 43rd International Symposium on Theoretical Aspects of Computer Science (STACS 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 364, pp. 77:1-77:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{saarela:LIPIcs.STACS.2026.77,
  author =	{Saarela, Aleksi},
  title =	{{An Improved Version of Hmelevskii’s Theorem on Three-Variable Word Equations}},
  booktitle =	{43rd International Symposium on Theoretical Aspects of Computer Science (STACS 2026)},
  pages =	{77:1--77:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-412-3},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{364},
  editor =	{Mahajan, Meena and Manea, Florin and McIver, Annabelle and Thắng, Nguy\~{ê}n Kim},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2026.77},
  URN =		{urn:nbn:de:0030-drops-255664},
  doi =		{10.4230/LIPIcs.STACS.2026.77},
  annote =	{Keywords: Combinatorics on words, word equation, parametric word}
}
Document
Track B: Automata, Logic, Semantics, and Theory of Programming
DOI: 10.4230/LIPIcs.ICALP.2020.120
The Post Correspondence Problem and Equalisers for Certain Free Group and Monoid Morphisms

Authors: Laura Ciobanu and Alan D. Logan

Published in: LIPIcs, Volume 168, 47th International Colloquium on Automata, Languages, and Programming (ICALP 2020)

Abstract
A marked free monoid morphism is a morphism for which the image of each generator starts with a different letter, and immersions are the analogous maps in free groups. We show that the (simultaneous) PCP is decidable for immersions of free groups, and provide an algorithm to compute bases for the sets, called equalisers, on which the immersions take the same values. We also answer a question of Stallings about the rank of the equaliser. Analogous results are proven for marked morphisms of free monoids.
Cite as

Laura Ciobanu and Alan D. Logan. The Post Correspondence Problem and Equalisers for Certain Free Group and Monoid Morphisms. In 47th International Colloquium on Automata, Languages, and Programming (ICALP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 168, pp. 120:1-120:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{ciobanu_et_al:LIPIcs.ICALP.2020.120,
  author =	{Ciobanu, Laura and Logan, Alan D.},
  title =	{{The Post Correspondence Problem and Equalisers for Certain Free Group and Monoid Morphisms}},
  booktitle =	{47th International Colloquium on Automata, Languages, and Programming (ICALP 2020)},
  pages =	{120:1--120:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-138-2},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{168},
  editor =	{Czumaj, Artur and Dawar, Anuj and Merelli, Emanuela},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2020.120},
  URN =		{urn:nbn:de:0030-drops-125271},
  doi =		{10.4230/LIPIcs.ICALP.2020.120},
  annote =	{Keywords: Post Correspondence Problem, marked map, immersion, free group, free monoid}
}
Document
Track B: Automata, Logic, Semantics, and Theory of Programming
DOI: 10.4230/LIPIcs.ICALP.2019.110
Solutions Sets to Systems of Equations in Hyperbolic Groups Are EDT0L in PSPACE (Track B: Automata, Logic, Semantics, and Theory of Programming)

Authors: Laura Ciobanu and Murray Elder

Published in: LIPIcs, Volume 132, 46th International Colloquium on Automata, Languages, and Programming (ICALP 2019)

Abstract
We show that the full set of solutions to systems of equations and inequations in a hyperbolic group, with or without torsion, as shortlex geodesic words, is an EDT0L language whose specification can be computed in NSPACE(n^2 log n) for the torsion-free case and NSPACE(n^4 log n) for the torsion case. Our work combines deep geometric results by Rips, Sela, Dahmani and Guirardel on decidability of existential theories of hyperbolic groups, work of computer scientists including Plandowski, Jeż, Diekert and others on PSPACE algorithms to solve equations in free monoids and groups using compression, and an intricate language-theoretic analysis. The present work gives an essentially optimal formal language description for all solutions in all hyperbolic groups, and an explicit and surprising low space complexity to compute them.
Cite as

Laura Ciobanu and Murray Elder. Solutions Sets to Systems of Equations in Hyperbolic Groups Are EDT0L in PSPACE (Track B: Automata, Logic, Semantics, and Theory of Programming). In 46th International Colloquium on Automata, Languages, and Programming (ICALP 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 132, pp. 110:1-110:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

Copy BibTex To Clipboard

@InProceedings{ciobanu_et_al:LIPIcs.ICALP.2019.110,
  author =	{Ciobanu, Laura and Elder, Murray},
  title =	{{Solutions Sets to Systems of Equations in Hyperbolic Groups Are EDT0L in PSPACE}},
  booktitle =	{46th International Colloquium on Automata, Languages, and Programming (ICALP 2019)},
  pages =	{110:1--110:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-109-2},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{132},
  editor =	{Baier, Christel and Chatzigiannakis, Ioannis and Flocchini, Paola and Leonardi, Stefano},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2019.110},
  URN =		{urn:nbn:de:0030-drops-106867},
  doi =		{10.4230/LIPIcs.ICALP.2019.110},
  annote =	{Keywords: Hyperbolic group, Existential theory, EDT0L language, PSPACE}
}
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