Base points of natural line bundles on relatively generic surface singularities

Abstract

In \cite{NNM} the author with A. N\'emethi computed the multiplicity of generic surface singularities, the formula is purely topological computable from the resolution graph of the surface singularity. In the present paper we extend the results partly to the relative case, when there is a pair of resolution graphs $\mathcal{T}_1 \subset \mathcal{T}$, a fixed singularity $\tX_1$ with resolution graph $\mathcal{T}_1$, a relatively generic singularity $\tX$ corresponding to the subsingularity $\tX_1$ with resolution graph $\mathcal{T}$. We determine the base points of the natural line bundles (under some mild conditions) on $\tX$ from the resolution graph $\mathcal{T}$ and the analytic invariants of the subsingularity $\tX_1$. For each base point $p$ we determine a lower bound for the number $t_p$ such that $p$ is $t_p$-simple and we compute from it a lower bound of the multiplicity of $\tX$, which is sharp in all known cases.