On directed local chromatic number, shift graphs, and Borsuk-like graphs

Abstract

We investigate the local chromatic number of shift graphs and prove that it is close to their chromatic number. This implies that the gap between the directed local chromatic number of an oriented graph and the local chromatic number of the underlying undirected graph can be arbitrarily large. We also investigate the minimum possible directed local chromatic number of oriented versions of “topologically t-chromatic” graphs. We show that this minimum for large enough t-chromatic Schrijver graphs and t-chromatic generalized Mycielski graphs of appropriate parameters is ⌈t/4⌉+1. © 2010 Wiley Periodicals, Inc. J Graph Theory 66: 65-82, 2010 © 2011 Wiley Periodicals, Inc.