ISSN 1234-3099 (print version)

ISSN 2083-5892 (electronic version)

Discussiones Mathematicae Graph Theory

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Discussiones Mathematicae Graph Theory


Discussiones Mathematicae Graph Theory 19(1) (1999) 93-110
DOI: 10.7151/dmgt.1088


E.J. Cockayne

Department of Mathematics, University of Victoria
P.O. Box 3045, Victoria, BC, CANADA V8W 3P4

C.M. Mynhardt

Department of Mathematics, University of South Africa
P.O. Box 392, Pretoria, South Africa 0003


A set X of vertices of a graph G is said to be 1-dependent if the subgraph of G induced by X has maximum degree one. The 1-dependent Ramsey number t1(l,m) is the smallest integer n such that for any 2-edge colouring (R,B) of Kn, the spanning subgraph B of Kn has a 1-dependent set of size l or the subgraph R has a 1-dependent set of size m. The 2-edge colouring (R,B) is a t1(l,m) Ramsey colouring of Kn if B (R, respectively) does not contain a 1-dependent set of size l (m, respectively); in this case R is also called a (l,m,n) Ramsey graph. We show that t1(4,5) = 9, t1(4,6) = 11, t1(4,7) = 16 and t1(4,8) = 17. We also determine all (4,4,5), (4,5,8), (4,6,10) and (4,7,15) Ramsey graphs.

Keywords: 1-dependence, irredundance, CO-irredundance, Ramsey numbers.

1991 Mathematics Subject Classification: 05C55, 05C70.


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Received 14 July 1998
Revised 12 April 1999