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Let $R$ be a Noetherian domain with fraction field $K$. Let $\overline{R}$ be the integral closure of $R$ in $K$. Is it possible to prove that $\overline{R}$ is a finitely generated $R$-module?

The condition of the original problem is that $R$ is a finitely generated module of its PID subring $S$.

MatrixBi
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    Here is a counterexample by Nagata when $R$ has dimension $3$. https://projecteuclid.org/journals/kyoto-journal-of-mathematics/volume-28/issue-2/Note-on-integral-closures-of-Noetherian-domains/10.1215/kjm/1250777425.full. In non-local case, there is counterexample even in dimension $1$. – mathmathmath Apr 19 '21 at 04:20

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Eisenbud has a discussion of this question in Section 13.3 of Commutative Algeba with a View Toward Algebraic Geometry, as does Matsumura in Section 33 of Commutative Ring Theory. If $R$ is a domain that is a finitely generated algebra over a field, then the integral closure of $R$ is finitely generated as an $R$-module. If $R$ is a complete Noetherian local domain, then the integral closure of $R$ is finitely generated as an $R$-module.

In 1935/6, Akizuki and Schmidt (separately) constructed examples of one-dimensional local Noetherian domains $R$ whose integral closure is not finitely generated as an $R$-module. There are many more examples known today. For instance, Goodearl and Lenagan gave a nice construction in 1989 of such examples here, though they are still a bit involved.

The Krull-Akizuki Theorem says that in the examples $R$ above (of dimension $1$), the integral closure is a Noetherian ring; this is also true if $R$ is $2$-dimensional. In 1953, at the link given by @mathmath, Nagata constructed a $3$-dimensional local Noetherian domain whose integral closure is not Noetherian.

Allen Bell
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