Homomorphisms, localizations and a new algorithm to construct invariant rings of finite groups

Let G be a finite group acting on a polynomial ring A over the field K and let AG denote the corresponding ring of invariants. Let B be the subalgebra of AG generated by all homogeneous elements of degree less than or equal to the group order G. Then in general B is not equal to AG if the characteristic of K divides G. However we prove that the field of fractions Quot(B) coincides with the field of invariants Quot(AG)=Quot(A)G. We also study various localizations and homomorphisms of modular invariant rings as tools to construct generators for AG. We prove that there is always a nonzero transfer c AG of degree