PNNL

Abstract

We consider the chromatic number of a family of graphs called box graphs, which arise from a box complex in n-space. It is straightforward to show that any box graph in the plane has an admissible coloring with three colors, and that any box graph in n-space has an admissible coloring with n + 1 colors. We show that for box graphs in n-space, if the lengths of the boxes in the corresponding box complex take on no more than two values from the set {1, 2, 3}, then the box graph is three-colorable, while for some graphs three colors are required. We also show that box graphs in 3-space which do not have cycles of length four (which we call "string complexes") are three-colorable.