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Weakly-exceptional quotient singularities

Dmitrijs Sakovics (2012)

Open Mathematics

A singularity is said to be weakly-exceptional if it has a unique purely log terminal blow-up. In dimension 2, V. Shokurov proved that weakly-exceptional quotient singularities are exactly those of types D n, E 6, E 7, E 8. This paper classifies the weakly-exceptional quotient singularities in dimensions 3 and 4.

Which weakly ramified group actions admit a universal formal deformation?

Jakub Byszewski, Gunther Cornelissen (2009)

Annales de l’institut Fourier

Consider a representation of a finite group G as automorphisms of a power series ring k [ [ t ] ] over a perfect field k of positive characteristic. Let D be the associated formal mixed-characteristic deformation functor. Assume that the action of G is weakly ramified, i.e., the second ramification group is trivial. Example: for a group action on an ordinary curve, the action of a ramification group on the completed local ring of any point is weakly ramified.We prove that the only such D that are not pro-representable...

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