TOPICS
Search

Choice Number


The choice number, or list chromatic number, of a finite simple graph G is the least nonnegative integer k such that every assignment of a list of k colors to each graph vertex permits a proper coloring that chooses the color of each graph vertex from its list.

The related partial list coloring conjecture concerned how many vertices can be properly colored when the lists are shorter than the choice number.

For an integer t>=3, Gu and Xu (2026, pp. 1-2) proved that finite simple graphs having no complete graph K_t as a graph minor have choice number O(tlnlnt). For such a graph on n vertices, they also obtained the bound O(tln(2+n/t)) where O denotes big-O notation and ln is the natural logarithm. Gu and Xu (2026) credit ChatGPT with discovering a key proposition and report using it for parameter choices and proof revisions. The authors checked the arguments and take responsibility for them.

The list color function counts the minimum number of allowed proper colorings over all list assignments of a fixed size. Equality of this function with the chromatic polynomial for every positive integer list size is enumerative chromatic choosability, a stronger condition than equality of choice number and chromatic number.

For a random graph G sampled from G(n,p) with np->infty, Wang and Zeng (2026) proved that its choice number is asymptotic to its chromatic number,

 ch(G)=(1+o(1))chi(G)

with high probability. This includes probabilities p tending to 1. Wang and Zeng (2026) attribute the uniform independent set argument to an AI-generated proof and report AI assistance with the dense case.

The Alon-Krivelevich conjecture predicted an upper bound ClnDelta for bipartite graphs of maximum vertex degree Delta>=2. Yu and Yu (2026) construct counterexamples satisfying

 ch(G)>=(1/(32)-o(1))((lnDelta)^2)/((lnlnDelta)^3).

The construction and proof were found with AI assistance and checked by the authors.

The strong fractional choice number instead requires list coloring with several colors selected at each graph vertex (Li and Zhu 2020).


See also

Chromatic Number, Correspondence Chromatic Number, Correspondence Coloring, Enumerative Chromatic Choosability, Graph Coloring, Graph Minor, Hadwiger Conjecture, List Color Function, List Coloring, Partial List Coloring Conjecture, Vertex Coloring

Explore with Wolfram|Alpha

References

Allred, S. and Mudrock, J. A. "Enumerative Chromatic Choosability." Elec. J. Combin. 33, P4.6, 2026. https://doi.org/10.37236/14176.Alon, N. and Krivelevich, M. "The Choice Number of Random Bipartite Graphs." Ann. Combin. 2, 291-297, 1998. https://doi.org/10.1007/BF01608526.Gu, Y. and Xu, R. "Improved Upper Bounds on the List Chromatic Number of K_t-Minor-Free Graphs." 1 Oct 2026. https://arxiv.org/abs/2610.01946v1.Li, X. and Zhu, X. "The Strong Fractional Choice Number of Series-Parallel Graphs." Disc. Math. 343, 111796, 2020. https://doi.org/10.1016/j.disc.2019.111796.Wang, L. and Zeng, J. "The Choice Number of Random Graphs." 26 Oct 2026. https://arxiv.org/abs/2610.35003.Yu, J. and Yu, G. "A Counterexample to the Alon-Krivelevich Conjecture and a New Lower Bound for Choosability of Bipartite Graphs." 30 Oct 2026. https://arxiv.org/abs/2610.42094v1.

Referenced on Wolfram|Alpha

Choice Number

Cite this as:

Weisstein, Eric W. "Choice Number." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/ChoiceNumber.html

Subject classifications