Seshadri constants and special configurations of points in the projective plane

In the present note, we focus on certain properties of special curves that might be used in the theory of multi-point Seshadri constants for ample line bundles on the complex projective plane. In particular, we provide three Ein-Lazarsfeld-Xu-type lemmas for plane curves and a lower bound on the multi-point Seshadri constant of ${\mathcal{O}}_{{\mathbb{P}}^2}(1)$ under the assumption that the chosen points are not very general. In the second part, we focus on certain arrangements of points in the plane which are given by line arrangements. We show that in some cases the multi-point Seshadri constants of ${\mathcal{O}}_{{\mathbb{P}}^2}(1)$ centered at singular loci of line arrangements are computed by lines from the arrangement having some extremal properties.