  We unify results of Artin, Brieskorn, Slodowy and others by showing that, in
all characteristics, the Artin component of the deformation space of a rational
surface singularity has a ramified cover where simultaneous resolution exists
and the Galois group of this cover is the Weyl group determined by the
configuration of $(-2)$-curves in the minimal resolution. This verifies a
conjecture made by Burns and Rapoport. We use an integral version of this to
show that certain actions of Weyl groups on polynomial rings over the integers
give rings of invariants that are also polynomial, and deduce that the integral
cohomology rings of complete flag varieties $G/B$ of types $A,D$ or $E$ can be
described as the corresponding rings of co-invariants.
