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Discrete Mathematics
Volume 152, Issues 1-3, 20 May 1996, Pages 295-298
 
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doi:10.1016/0012-365X(95)00349-2    
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Copyright © 1996 Published by Elsevier Science B.V.

Communication

A triangle-free circle graph with chromatic number 5

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A. A. Ageev1

Institute of Mathematics, Universitetskii pr. 4, Novosibirsk 630090, Russia


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 4less-than-or-equals, slantχ* less-than-or-equals, slant5 where χ* = max gc(G): G is a triangle-free circle graph. We show that χ* greater-or-equal, slanted 5 and thus χ* = 5. This disproves the conjecture of Karapetyan that χ* = 4 and answers negatively a question of Gyárfás and Lehel.

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1 Partially supported by the Russian Foundation for Fundamental Research, grant 93-011-1486.


Discrete Mathematics
Volume 152, Issues 1-3, 20 May 1996, Pages 295-298
 
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