$2$-arcs of maximal size in the affine and the projective Hjelmslev plane over ${\mathbb{Z}}_{25}$

Michael Kiermaier, Matthias Koch, Sascha Kurz

It is shown that the maximal size of a $2$-arc in the projective Hjelmslev plane over ${\mathbb{Z}}_{25}$ is $21$, and the $(21,2)$-arc is unique up to isomorphism. Furthermore, all…