Generalizing Korchmáros--Mazzocca arcs

Abstract

In this paper, we generalize the so called Korchmáros--Mazzocca arcs, that is, point sets of size $q+t$ intersecting each line in $0,2$ or $t$ points in a finite projective plane of order $q$. For $t\ne 2$, this means that each point of the point set is incident with exactly one line meeting the point set in $t$ points. In $\mathrm{PG}(2,p^n)$, we change $2$ in the definition above to any integer $m$ and describe all examples when $m$ or $t$ is not divisible by $p$. We also study mod $p$ variants of these objects, give examples and under some conditions we prove the existence of a nucleus.

To appear in Combinatorica