On the upper and lower chromatic numbers of BSQSs(16)
A \(\text{BSQS}(16)\) is a Steiner quadruple system on 16 vertices, considered as a mixed hypergraph with each block belonging to both classes. Accordingly it is asked for vertex colourings of \(\text{BSQSs}(16)\) such that in each block not all the vertices are equally coloured and not all are differently coloured. It is shown that each \(\text{BSQS}(16)\) is colourable that way and that in any case the maximum number of colours is three, while the minimum number may be two or three, both cases occurring.
scientific article; zbMATH DE number 1557044