  The main result of this paper is a generalization of the theorem of
Chevalley-Shephard-Todd to the rings of invariants of pseudoreflection groups
over Dedekind domains. In the special case of a principal ideal domain in which
the group order is invertible it is proved that this ring of invariants is
isomorphic to a polynomial ring. An intermediate result is that every finitely
generated regular graded algebra over a Dedekind domain is isomorphic to a
tensor product of blowup algebras.
