On balanced incomplete block designs with specified weak chromatic number

Abstract

A weak $c$-colouring of a balanced incomplete block design (BIBD) is a colouring of the points of the design with $c$ colours in such a way that no block of the design has all of its vertices receive the same colour. A BIBD is said to be weakly $c$-chromatic if $c$ is the smallest number of colours with which the design can be weakly coloured. In this paper we show that for all $c\ge 2$ and $k\ge 3$ with $(c,k)\ne (2,3)$, the obvious necessary conditions for the existence of a $(v,k,\lambda )$-BIBD are asymptotically sufficient for the existence of a weakly $c$-chromatic $(v,k,\lambda )$-BIBD.

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