Fedder-type criterion for quasi--splitting and quasi--regularity
arXiv:2505.09015
Abstract
We study quasi--split and quasi--regular singularities, which generalize Yobuko's quasi--splitting. We establish Fedder type criteria that characterize these properties for hypersurfaces. These criteria offer explicit tools for computation and verification. As an application, we construct a counterexample to the inversion of adjunction for quasi--regularity and compute the quasi--split threshold of the cone over the ordinary cusp.
26 pages, v3:I added Section 6 on the quasi--split threshold