Abstract
A ring extension R ⊆ S is said to be strongly affine if each R-subalgebra of S is a finite-type R-algebra. In this paper, several characterizations of strongly affine extensions are given. For instance, we establish that if R is a quasi-local ring of finite dimension, then R ⊆ S is integrally closed and strongly affine if and only if R ⊆ S is a Prufer extension (i.e. (R, S) is a normal pair). As a consequence, the equivalence of strongly affine extensions, quasi-Prufer extensions and INC-pairs is shown. Let G be a subgroup of the automorphism group of S such that R is invariant under action by G. If R ⊆ S is strongly affine, then RG ⊆ SG is strongly affine under some conditions.
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