Recognition: 2 theorem links
· Lean TheoremConflict-Free Cuts in Planar and 3-Degenerate Graphs with 1-Regular Conflicts
Pith reviewed 2026-05-13 04:45 UTC · model grok-4.3
The pith
Every planar 4-regular graph except the octahedron admits a conflict-free cut when edge conflicts form disjoint pairs.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
For any 1-regular conflict graph on the edges, every planar 4-regular graph other than the octahedron graph possesses a conflict-free cut. The decision problem of whether a conflict-free cut exists is NP-complete both for planar graphs of maximum degree 5 and for 3-degenerate graphs of maximum degree 5. Infinite families of graphs equipped with 1-regular conflict graphs that admit no conflict-free cut are constructed.
What carries the argument
A conflict-free cut: a disconnecting edge subset that contains at most one edge from each conflicting pair in the given 1-regular conflict graph on the edge set.
If this is right
- Conflict-free cuts exist in every planar 4-regular graph except the octahedron.
- Deciding existence of a conflict-free cut is NP-complete for planar graphs of maximum degree 5.
- Deciding existence of a conflict-free cut is NP-complete for 3-degenerate graphs of maximum degree 5.
- There exist infinite families of graphs with 1-regular conflicts that have no conflict-free cut whatsoever.
Where Pith is reading between the lines
- The degree-4 guarantee indicates that planarity plus regularity together force the existence of a constrained disconnecting set.
- The jump to NP-completeness at degree 5 shows that one additional incident edge per vertex supplies enough freedom for hardness reductions while preserving planarity or 3-degeneracy.
- Analogous thresholds may exist for other sparse classes such as bounded-treewidth or series-parallel graphs.
Load-bearing premise
The conflicts between edges form a perfect matching of disjoint pairs.
What would settle it
A planar 4-regular graph distinct from the octahedron together with a 1-regular conflict assignment on its edges that admits no conflict-free cut would refute the existence claim.
Figures
read the original abstract
A conflict-free cut $F$ on a simple connected graph $G = (V, E)$ is defined as a set of edges $F \subseteq E$ such that $G-F$ is disconnected, and no two edges in $F$ are conflicting. The notion of conflicting edges is represented using an associated conflict graph $\widehat{G} = (\widehat{V}, \widehat{E})$ where $\widehat{V} = E$. Deciding if a given planar graph $G$, with an associated conflict graph $\widehat{G}$, has a conflict-free cut is known to be NP-complete, when $G$ has maximum degree four and $\widehat{G}$ is a line graph of $G$ [Bonsma, JGT 2009]. In this paper, we prove the following for the case when $\widehat{G}$ is 1-regular. * We completely resolve the complexity of the decision problem when $G$ is planar. Towards this end, we show that (a) there always exists a conflict-free cut when the graph is planar and 4-regular unless it is the octahedron graph and (b) the decision problem is NP-complete, even in the case when $G$ is planar with maximum degree 5. * We also show that the decision problem is NP-complete when $G$ is a 3-degenerate graph with maximum degree 5. This completely resolves the complexity status of the problem when $G$ is 3-degenerate. * We construct families of graphs with 1-regular conflict graphs that do not have a conflict-free cut. Our results answer the questions posed in [Rauch, Rautenbach and Souza, IPL 2025].
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript studies conflict-free cuts (edge sets whose removal disconnects the graph with no two edges conflicting) under the restriction that the conflict graph is exactly 1-regular. It proves that every planar 4-regular graph admits a conflict-free cut except the octahedron; shows that deciding existence is NP-complete for planar graphs of maximum degree 5; proves NP-completeness for 3-degenerate graphs of maximum degree 5; and constructs infinite families of graphs with 1-regular conflicts that have no conflict-free cut. These results resolve the open questions left by Rauch, Rautenbach and Souza (IPL 2025).
Significance. If the proofs hold, the work completely settles the complexity status of the conflict-free cut problem for all planar graphs and all 3-degenerate graphs when conflicts are 1-regular. The structural existence theorem for 4-regular planar graphs is strong and clean, while the two NP-completeness results close the remaining cases left open by prior hardness proofs that used line graphs or unrestricted conflicts. The explicit constructions of graphs without conflict-free cuts supply concrete negative examples and boundary cases.
minor comments (3)
- Abstract: a one-sentence indication of the main proof techniques (e.g., “by Eulerian orientation and matching arguments” or “by planar gadget reduction from 3-SAT”) would help readers gauge the approach without reading the full text.
- The manuscript should include a small illustrative figure (perhaps in the construction section) showing one member of the infinite family of graphs without conflict-free cuts.
- Ensure that the bibliographic entry for the 2025 IPL paper is complete and that all cross-references to prior work on line-graph conflicts are consistent.
Simulated Author's Rebuttal
We thank the referee for their positive summary, significance assessment, and recommendation of minor revision. The report confirms that our results resolve the open questions from Rauch, Rautenbach and Souza (IPL 2025) for planar and 3-degenerate graphs under 1-regular conflicts. Since no specific major comments or requested changes were listed, we provide no point-by-point responses below.
Circularity Check
No significant circularity detected
full rationale
The paper establishes an existence theorem for conflict-free cuts in planar 4-regular graphs (except the octahedron) via direct case analysis and constructs explicit NP-completeness reductions for planar max-degree-5 and 3-degenerate max-degree-5 graphs using new gadgets that preserve the 1-regular conflict condition. These steps are self-contained mathematical arguments that do not reduce to prior fitted parameters, self-defined quantities, or load-bearing self-citations. The only external reference is to Rauch et al. (IPL 2025), which merely poses the open questions resolved here; no ansatz, uniqueness theorem, or renaming of known results is imported from overlapping authors. The derivation chain therefore stands on independent proofs and reductions.
Axiom & Free-Parameter Ledger
axioms (1)
- standard math Standard definitions and basic properties of planar graphs, 3-degenerate graphs, and 1-regular graphs hold.
Lean theorems connected to this paper
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IndisputableMonolith/Foundation/AlexanderDuality.leanalexander_duality_circle_linking unclearWe show that (a) there always exists a conflict-free cut when the graph is planar and 4-regular unless it is the octahedron graph and (b) the decision problem is NP-complete, even in the case when G is planar with maximum degree 5.
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IndisputableMonolith/Foundation/ArithmeticFromLogic.leanLogicNat induction unclearWe also show that the decision problem is NP-complete when G is a 3-degenerate graph with maximum degree 5.
Reference graph
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