Du Val singularity
ISOLATED SINGULARITY OF A COMPLEX SURFACE
Kleinian singularity; Rational double point; Simple surface singularity; Simple singularity; DuVal singularity; Klein singularity; Du Val singularities; Cyclic singularity
In algebraic geometry, a Du Val singularity, also called simple surface singularity, Kleinian singularity, or rational double point, is an isolated singularity of a complex surface which is modeled on a double branched cover of the plane, with minimal resolution obtained by replacing the singular point with a tree of smooth rational curves, with intersection pattern dual to a Dynkin diagram of A-D-E singularity type. They are the canonical singularities (or, equivalently, rational Gorenstein singularities) in dimension 2.