Simpler and More General Distributed Coloring Based on Simple List Defective Coloring Algorithms
Pith reviewed 2026-05-24 00:57 UTC · model grok-4.3
The pith
Two sweeps over an oriented graph solve list defective coloring when lists have size p² and satisfy a defect sum condition.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
If all nodes have lists of size p² and ∀v: ∑_{x∈L_v}(d_v(x)+1) > p·β, then two sweeps of the nodes in opposite order over an edge-oriented graph with maximum outdegree β let each node v choose a color x∈L_v such that at most d_v(x) outneighbors of v receive color x. This generalizes known defective coloring results and supplies new distributed algorithms for standard coloring problems.
What carries the argument
The two-sweep procedure on an edge-oriented graph that assigns colors from lists to meet per-color outneighbor defect bounds under the p² list-size and defect-sum conditions.
If this is right
- Yields an alternative Õ(√Δ) + O(log* n)-round algorithm for (Δ+1)-coloring in the CONGEST model.
- Extends the single-sweep defective coloring approach to the list setting for graphs of neighborhood independence θ.
- Produces a (log Δ)^{O(log log Δ)} + O(log* n)-round algorithm when θ is constant.
- Supplies list defective coloring that is simpler and computationally faster than previous methods.
Where Pith is reading between the lines
- The two-sweep method might combine with other orientation strategies to improve round complexity in additional models.
- List defective coloring could serve as a building block for distributed solutions to further sparse graph problems.
- The simplicity of the sweeps may allow direct implementation without heavy preprocessing in restricted communication settings.
Load-bearing premise
The graph admits an edge orientation with maximum outdegree β and the lists satisfy the size p² and per-node defect-sum conditions.
What would settle it
A concrete graph, orientation of outdegree β, and lists of size p² with all defect sums > p β such that after two sweeps at least one node exceeds its allowed defect for the chosen color.
Figures
read the original abstract
In this paper, we give list coloring variants of simple iterative defective coloring algorithms. Formally, in a list defective coloring instance, each node $v$ of a graph is given a list $L_v$ of colors and a list of allowed defects $d_v(x)$ for the colors. Each node $v$ needs to be colored with a color $x\in L_v$ such that at most $d_v(x)$ neighbors of $v$ also pick the same color $x$. For a defect parameter $d$, it is known that by making two sweeps in opposite order over the nodes of an edge-oriented graph with maximum outdegree $\beta$, one can compute a coloring with $O(\beta^2/d^2)$ colors such that every node has at most $d$ outneighbors of the same color. We generalize this and show that if all nodes have lists of size $p^2$ and $\forall v:\sum_{x\in L_v}(d_v(x)+1)>p\cdot\beta$, we can make two sweeps of the nodes such that at the end, each node $v$ has chosen a color $x\in L_v$ for which at most $d_v(x)$ outneighbors of $v$ are colored with color $x$. Our algorithm is simpler and computationally significantly more efficient than existing algorithms for similar list defective coloring problems. We show that the above result can in particular be used to obtain an alternative $\tilde{O}(\sqrt{\Delta})+O(\log^* n)$-round algorithm for the $(\Delta+1)$-coloring problem in the CONGEST model. The neighborhood independence $\theta$ of a graph is the maximum number of pairwise non-adjacent neighbors of some node of the graph. It is known that by doing a single sweep over the nodes of a graph of neighborhood independence $\theta$, one can compute a $d$-defective coloring with $O(\theta\cdot \Delta/d)$ colors. We extend this approach to the list defective coloring setting and use it to obtain an efficient recursive coloring algorithm for graphs of neighborhood independence $\theta$. In particular, if $\theta=O(1)$, we get an $(\log\Delta)^{O(\log\log\Delta)}+O(\log^* n)$-round algorithm.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper gives list-defective variants of known iterative defective-coloring procedures. The central result states that, given an orientation of maximum out-degree β together with per-node lists L_v of size p² satisfying ∑_{x∈L_v}(d_v(x)+1) > p·β for every v, two sweeps (in opposite order) produce a coloring in which each v selects x∈L_v with at most d_v(x) out-neighbors also colored x. The same technique is extended to a single-sweep list-defective procedure on graphs of neighborhood independence θ. These primitives are used to obtain an alternative Õ(√Δ)+O(log* n)-round (Δ+1)-coloring algorithm in CONGEST and a (log Δ)^{O(log log Δ)}+O(log* n)-round algorithm when θ=O(1).
Significance. If the stated conditions hold, the work supplies a simpler, parameter-light constructive procedure for list defective coloring that directly yields known round-complexity bounds for (Δ+1)-coloring and improves the state of the art for bounded-neighborhood-independence graphs. The arithmetic contradiction argument (if every color violated its defect bound then the sum of counts would exceed both the list-size and out-degree bounds) is a clear strength; the absence of fitted parameters or self-referential definitions makes the result easy to apply as a black-box primitive.
minor comments (2)
- The manuscript should explicitly state whether the required edge orientation of out-degree ≤β is assumed to be given as part of the input or must be computed inside the CONGEST algorithm; a one-sentence clarification in §3 would remove ambiguity for implementers.
- Notation for the two opposite-order sweeps is introduced only in the abstract; adding a short pseudocode block or a numbered paragraph in the main body would make the reduction from the non-list case to the list case easier to follow.
Simulated Author's Rebuttal
We thank the referee for the positive assessment and recommendation to accept. The review accurately captures the contributions of our list-defective coloring primitives and their applications to CONGEST coloring.
Circularity Check
No significant circularity
full rationale
The paper's core result is a direct constructive generalization of the two-sweep out-defective coloring procedure to the list-defective setting. The key existence argument at each node is a self-contained counting contradiction: if every color x satisfied count_x >= d_v(x)+1 then sum count_x >= sum(d_v(x)+1) > p beta, contradicting the out-degree bound beta. This arithmetic holds independently of processing order and does not rely on fitted parameters, self-referential definitions, or load-bearing self-citations. The neighborhood-independence extension follows from an analogous single-sweep counting argument. The derivation is therefore self-contained against the stated premises.
Axiom & Free-Parameter Ledger
axioms (2)
- standard math Every graph admits an orientation with maximum outdegree equal to its maximum degree
- domain assumption The list-size and defect-sum conditions are supplied as input
Reference graph
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