Computational complexity of covering coloured mixed multigraphs with simple degree partitions.

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Title: Computational complexity of covering coloured mixed multigraphs with simple degree partitions.
Authors: Bok, Jan1,2 (AUTHOR) jan.bok@matfyz.cuni.cz, Fiala, Jiří1,3 (AUTHOR) fiala@kam.mff.cuni.cz, Jedličková, Nikola1,3 (AUTHOR) jedlickova@kam.mff.cuni.cz, Kratochvíl, Jan1,3 (AUTHOR) honza@kam.mff.cuni.cz, Seifrtová, Michaela1,3 (AUTHOR) michaela.seifrtova@mff.cuni.cz
Source: Discrete Applied Mathematics. May2026, Vol. 385, p194-221. 28p.
Subjects: Computational complexity, Multigraph, NP-hard problems, Graph theory
Abstract: The notion of graph covers (also referred to as locally bijective homomorphisms) plays an important role in topological graph theory and has found its computer science applications in models of local computation. For a fixed target graph H , the H - Cover problem asks if an input graph G allows a graph covering projection onto H. Despite the fact that the quest for characterizing the computational complexity of H - Cover had been started more than 30 years ago, only a handful of general results have been known so far. In this paper, we present a complete characterization of the computational complexity of covering coloured graphs for the case that every equivalence class in the degree partition of the target graph has at most two vertices. We prove this result in a very general form. Following the lines of current development of topological graph theory, we study graphs in the most relaxed sense of the definition. In particular, we consider graphs that are mixed (they may have both directed and undirected edges), may have multiple edges, loops, and semi-edges. We show that a strong P/NP-complete dichotomy holds true in the sense that for each such fixed target graph H , the H - Cover problem is either polynomial-time solvable for arbitrary inputs, or NP-complete even for simple input graphs. [ABSTRACT FROM AUTHOR]
Copyright of Discrete Applied Mathematics is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Computational complexity of covering coloured mixed multigraphs with simple degree partitions.
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  Data: <searchLink fieldCode="AR" term="%22Bok%2C+Jan%22">Bok, Jan</searchLink><relatesTo>1,2</relatesTo> (AUTHOR)<i> jan.bok@matfyz.cuni.cz</i><br /><searchLink fieldCode="AR" term="%22Fiala%2C+Jiří%22">Fiala, Jiří</searchLink><relatesTo>1,3</relatesTo> (AUTHOR)<i> fiala@kam.mff.cuni.cz</i><br /><searchLink fieldCode="AR" term="%22Jedličková%2C+Nikola%22">Jedličková, Nikola</searchLink><relatesTo>1,3</relatesTo> (AUTHOR)<i> jedlickova@kam.mff.cuni.cz</i><br /><searchLink fieldCode="AR" term="%22Kratochvíl%2C+Jan%22">Kratochvíl, Jan</searchLink><relatesTo>1,3</relatesTo> (AUTHOR)<i> honza@kam.mff.cuni.cz</i><br /><searchLink fieldCode="AR" term="%22Seifrtová%2C+Michaela%22">Seifrtová, Michaela</searchLink><relatesTo>1,3</relatesTo> (AUTHOR)<i> michaela.seifrtova@mff.cuni.cz</i>
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  Data: <searchLink fieldCode="JN" term="%22Discrete+Applied+Mathematics%22">Discrete Applied Mathematics</searchLink>. May2026, Vol. 385, p194-221. 28p.
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  Data: <searchLink fieldCode="DE" term="%22Computational+complexity%22">Computational complexity</searchLink><br /><searchLink fieldCode="DE" term="%22Multigraph%22">Multigraph</searchLink><br /><searchLink fieldCode="DE" term="%22NP-hard+problems%22">NP-hard problems</searchLink><br /><searchLink fieldCode="DE" term="%22Graph+theory%22">Graph theory</searchLink>
– Name: Abstract
  Label: Abstract
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  Data: The notion of graph covers (also referred to as locally bijective homomorphisms) plays an important role in topological graph theory and has found its computer science applications in models of local computation. For a fixed target graph H , the H - Cover problem asks if an input graph G allows a graph covering projection onto H. Despite the fact that the quest for characterizing the computational complexity of H - Cover had been started more than 30 years ago, only a handful of general results have been known so far. In this paper, we present a complete characterization of the computational complexity of covering coloured graphs for the case that every equivalence class in the degree partition of the target graph has at most two vertices. We prove this result in a very general form. Following the lines of current development of topological graph theory, we study graphs in the most relaxed sense of the definition. In particular, we consider graphs that are mixed (they may have both directed and undirected edges), may have multiple edges, loops, and semi-edges. We show that a strong P/NP-complete dichotomy holds true in the sense that for each such fixed target graph H , the H - Cover problem is either polynomial-time solvable for arbitrary inputs, or NP-complete even for simple input graphs. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
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  Data: <i>Copyright of Discrete Applied Mathematics is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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RecordInfo BibRecord:
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        Value: 10.1016/j.dam.2026.01.019
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      – Code: eng
        Text: English
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        PageCount: 28
        StartPage: 194
    Subjects:
      – SubjectFull: Computational complexity
        Type: general
      – SubjectFull: Multigraph
        Type: general
      – SubjectFull: NP-hard problems
        Type: general
      – SubjectFull: Graph theory
        Type: general
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      – TitleFull: Computational complexity of covering coloured mixed multigraphs with simple degree partitions.
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            NameFull: Bok, Jan
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            NameFull: Fiala, Jiří
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            NameFull: Jedličková, Nikola
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            NameFull: Kratochvíl, Jan
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            – D: 31
              M: 05
              Text: May2026
              Type: published
              Y: 2026
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