# Noon lecture

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On 12.06.2008 at 12:20 in S3, there is the following noon lecture:

# Circular choosability is rational

## Tobias Mueller

## Technische Universiteit Eindhoven

## Abstract

The circular chromatic number of a graph is a refinement of the ordinary chromatic number that has attracted considerable attention since its introduction by Vince in 1988. One of the nice properties it enjoys that it is a rational number that lies between the chromatic number and the chromatic number minus one.

In 2002 Mohar introduced a ``list version'' of the circular chromatic number, the circular choosability. After a brief overview of known results and open problems on circular choosability, I will give a proof of the (nontrivial) fact that the circular choosability is a rational number for all graphs.

list of noon lectures ( 2005 | 2006 | 2007 | 2008 | 2009 | 2010 | 2011 | 2012 | 2013 | 2014 | 2015 | 2016 | 2017 | 2018 | 2019 | future lectures)

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