Copyright © 1996 Published by Elsevier Science B.V.
Communication
A triangle-free circle graph with chromatic number 5
Received 20 November 1995.
Communicated by D.R. Woodall
Available online 9 February 1999.
Abstract
It follows from the results of Karapetyan (1984), Gyárfás and Lehel (1985), and Kostochka (1988) that 4
χ*
5 where χ* = max gc(G): G is a triangle-free circle graph. We show that χ*
5 and thus χ* = 5. This disproves the conjecture of Karapetyan that χ* = 4 and answers negatively a question of Gyárfás and Lehel.
Article Outline
1 Partially supported by the Russian Foundation for Fundamental Research, grant 93-011-1486.






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