On infinitesimal deformations and obstructions for rational surface singularities

The purpose of this paper is to prove dimension formulas for $T^1$ and $T^2$ for rational surface singularities. These modules play an important role in the deformation theory of isolated singularities in analytic and algebraic geometry. The first may be identified as the Zariski tangent space of the versal deformation of the singularity; i.e. it is the space of infinitesimal deformations. The second contains the obstruction space – in all known cases it is the whole obstruction space for rational surface singularities.