Flexibility of Planar Graphs -- Sharpening the Tools to Get Lists of Size Four

Ilkyoo Choi, Felix Christian Clemen, Michael Ferrara +3

A graph where each vertex $v$ has a list $L(v)$ of available colors is $L$-colorable if there is a proper coloring such that the color of $v$ is in $L(v)$ for each $v$. A graph is…