Sufficiency of Hall's Condition for Graphic List Coloring

Abstract

For finite simple graphs $G,H$ on a common vertex set $V$, we say that $H$ is $G$-colorable if $H$ admits a proper list coloring with list assignment $L(v)=N_G(v)$ for all $v\in V$. This notion of coloring a graph using the neighborhood of another graph on the same vertex set, which we call \emph{graphic list coloring}, has connections to several classical topics, including systems of distinct representatives and graph factorizations. In this paper, we investigate when a necessary Hall-type condition, introduced by Hilton and Johnson in 1990, is also sufficient for $H$ to be $G$-colorable. We characterize all graphs $H$ that are $G$-colorable whenever the pair $(H,G)$ satisfies Hall's condition, answering a question raised by Johnson. We then consider the dual problem of characterizing graphs $G$ such that, whenever $(H,G)$ satisfies Hall's condition, $H$ is $G$-colorable. In this vein, we obtain complete results for several families of graphs, such as forests, complete multipartite graphs, and grid graphs.