Distant 2-Colored Components on Embeddings Part II: The Short-Inseparable Case

TL;DR

This paper extends Thomassen's 5-choosability theorem to graphs on surfaces with distant 2-colored components, proving the result for certain embeddings with large face-width and separation conditions.

Contribution

It generalizes Thomassen's conjecture to a broader class of embeddings with specific triangulation and cycle restrictions.

Findings

Proves 5-choosability for graphs with distant 2-colored components on surfaces.

Establishes conditions on face-width and component separation for the theorem.

Extends previous results to embeddings satisfying certain triangulation and cycle length constraints.

Abstract

This is the second in a sequence of three papers in which we prove the following generalization of Thomassen's 5-choosability theorem: Let $G$ be a graph embedded on a surface of genus $g$. Then $G$ can be $L$-colored, where $L$ is a list-assignment for $G$ in which every vertex has a 5-list except for a collection of pairwise far-apart components, each precolored with an ordinary 2-coloring, as long as the face-width of $G$ is at least $2^{\Omega(g)}$ and the precolored components are of distance at least $2^{\Omega(g)}$ apart. This provides an affirmative answer to a generalized version of a conjecture of Thomassen and also generalizes a result from 2017 of Dvo\v{r}\'ak, Lidick\'y, Mohar, and Postle about distant precolored vertices. In this paper we prove that the above result holds for a restricted class of embeddings, i.e. those embeddings which satisfy certain triangulation conditions and do not have separating cycles of length at most four.