List Colouring Squares of Planar Graphs

Abstract

In 1977, Wegner conjectured that the chromatic number of the square of every planar graph $G$ with maximum degree $\Delta\ge8$ is at most $\bigl\lfloor\frac32\Delta\bigr\rfloor+1$. We show that it is at most $\frac32 \Delta (1+o(1))$ (where the $o(1)$ is as $\Delta\to+\infty$), and indeed that this is true for the list chromatic number and for more general classes of graphs.