Improved lower bounds on the number of edges in list critical and online list critical graphs

TL;DR

This paper establishes improved lower bounds on the number of edges in list critical and online list critical graphs for k ≥ 7, advancing previous bounds by Kostochka, Stiebitz, Riasat, and Schauz.

Contribution

It introduces tighter lower bounds on edges in k-list-critical and online k-list-critical graphs, extending prior results with a new general theorem involving Alon-Tarsi orientable subgraphs.

Findings

New lower bounds for edges in k-list-critical graphs

Enhanced bounds for online k-list-critical graphs

General theorem linking edge count to Alon-Tarsi orientability

Abstract

We prove that every $k$-list-critical graph ($k \ge 7$) on $n \ge k+2$ vertices has at least $\frac12 \left(k-1 + \frac{k-3}{(k-c)(k-1) + k-3}\right)n$ edges where $c = (k-3)\left(\frac12 - \frac{1}{(k-1)(k-2)}\right)$. This improves the bound established by Kostochka and Stiebitz. The same bound holds for online $k$-list-critical graphs, improving the bound established by Riasat and Schauz. Both bounds follow from a more general result stating that either a graph has many edges or it has an Alon-Tarsi orientable induced subgraph satisfying a certain degree condition.