**Theorem**: Assume that X is either spherical or affine. Then the center Z(X) of the ring of G-invariant differential operators on X is a polynomial ring. More precisely, Z(X) is isomorphic to the ring of invariants of a finite reflection group.},
author = {Knop, Friedrich},
doi = {10.2307/2118600},
faupublication = {no},
journal = {Annals of Mathematics},
pages = {253-288},
peerreviewed = {Yes},
title = {{A} {Harish}-{Chandra} homomorphism for reductive group actions},
volume = {140},
year = {1994}
}