Upper chromatic number of generalized quadrangles

Abstract

We can regard a generalized quadrangle as a hypergraph in which points and lines are identified with vertices and hyperedges, respectively. A vertex coloring is said to be rainbow on a hyperedge if all vertices contained in that hyperedge are assigned pairwise distinct colors; if no hyperedge is rainbow, the coloring is termed rainbow-free. For a given hypergraph $H$, the maximum integer $k$ for which there exists a rainbow-free $k$-coloring is called the upper chromatic number of $H$, and is denoted by $\overlineχ(H)$.