Abstract
We study c-crossing-critical graphs, which are the minimal graphs that require at least c edge-crossings when drawn in the plane. For every fixed pair of integers with c ≥ 13 and d ≥ 1, we give first explicit constructions of c-crossing-critical graphs containing arbitrarily many vertices of degree greater than d. We also show that such unbounded degree constructions do not exist for c ≤ 12, precisely, that there exists a constant D such that every c-crossing-critical graph with c ≤ 12 has maximum degree at most D. Hence, the bounded maximum degree conjecture of c-crossing-critical graphs, which was generally disproved in 2010 by Dvořák and Mohar (without an explicit construction), holds true, surprisingly, exactly for the values c ≤ 12.1
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We acknowledge the supporting environment of the workshop Crossing Numbers: Theory and Applications (18w5029) at the Banff International Research Station, where the fundamentals of this contribution were developed.
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Drago Bokal was supported by ARRS Projects J1-8130, J1-2452 and ARRS Programme P1-0297.
Zdenĕk Dvořák was supported by project 17-04611S (Ramsey-like aspects of graph coloring) of Czech Science Foundation.
Petr Hlinĕný was supported by projects 17-00837S and 20-04567S of Czech Science Foundation.
Jesús Leaños was partially supported by PFCE-UAZ 2018-2019 grant.
Bojan Mohar was supported in part by the NSERC Discovery Grant R611450 (Canada), by the Canada Research Chairs program, and by the Research Projects J1-8130 and J1-2452 of ARRS (Slovenia).
Tilo Wiedera was supported by the German Research Foundation (DFG) project CH 897/2-2.
This work is based on a SoCG contribution [9] and gives full proofs and a significant strengthening of the announced results.
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Bokal, D., Dvořák, Z., Hlinĕný, P. et al. Bounded Degree Conjecture Holds Precisely for c-Crossing-Critical Graphs with c ≤ 12. Combinatorica 42, 701–728 (2022). https://doi.org/10.1007/s00493-021-4285-3
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DOI: https://doi.org/10.1007/s00493-021-4285-3