,
Ken-ichi Kawarabayashi
,
Stephan Kreutzer
Creative Commons Attribution 4.0 International license
We prove that every class of Eulerian directed graphs of bounded carving width (equivalently, of bounded degree and treewidth) is well-quasi-ordered by strong immersion. In fact, we prove a stronger result, namely that every class of Eulerian directed graphs of bounded carving width, where every vertex is additionally labelled from a well-quasi-order, fixes a linear order on its incident edges, and may impose further restrictions on how the immersion is allowed to route paths through it, is well-quasi-ordered by an adequate notion of strong immersion. To this extent, we develop a framework seemingly suited to prove well-quasi-ordering for classes of Eulerian directed graphs by (strong) immersion and present a first meta theorem in that direction. We complement our results by observing that the class of Eulerian directed graphs of unbounded degree is not well-quasi-ordered by strong immersion, even if we assume the treewidth of the class to be at most two. We conclude with a dichotomy result, proving for a very restricted class of Eulerian directed graphs of unbounded degree that it is not well-quasi-ordered by strong immersion, but it is well-quasi-ordered by weak immersion.
@InProceedings{cavallaro_et_al:LIPIcs.ICALP.2026.51,
author = {Cavallaro, Dario and Kawarabayashi, Ken-ichi and Kreutzer, Stephan},
title = {{Well-Quasi-Ordering Eulerian Digraphs: Bounded Carving Width}},
booktitle = {53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026)},
pages = {51:1--51:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-428-4},
ISSN = {1868-8969},
year = {2026},
volume = {374},
editor = {Bhattacharya, Sayan and Nanongkai, Danupon and Benedikt, Michael and Puppis, Gabriele},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2026.51},
URN = {urn:nbn:de:0030-drops-264404},
doi = {10.4230/LIPIcs.ICALP.2026.51},
annote = {Keywords: algorithmic graph theory, structural graph theory, digraphs, immersions, well-quasi ordering}
}