The packing chromatic number of the square lattice is at least 12

Jan Ekstein, Jiří Fiala, Přemysl Holub +1

The packing chromatic number ${\chi }_{\rho }(G)$ of a graph $G$ is the smallest integer $k$ such that the vertex set $V(G)$ can be partitioned into disjoint classes $X_1,...,X_k$, where ver…