Bourbaki

Exercise 6, § 3

Commutative Algebra, V, 372

An integral domain AA is called integrally Noetherian if it is Noetherian and if, for every finite sequence (ti)1≤i≤n(t_i)_{1 \leq i \leq n} of elements of an extension field of the field of fractions of AA, the integral closure of A[t1,…,tn]A[t_1, \ldots, t_n] is a finitely generated A[t1,…,tn]A[t_1, \ldots, t_n]-module. Every finitely generated integral algebra over a field is an integrally Noetherian domain (no. 2, Theorem 2).

(a) Every finitely generated integral algebra over an integrally Noetherian domain is an integrally Noetherian domain. Every ring of fractions of an integrally Noetherian domain not reduced to 0 is an integrally Noetherian domain.

(b) Let AA be an integrally Noetherian domain (ti)1≤i≤n(t_i)_{1 \leq i \leq n} a finite sequence of elements of an extension field of the field of fractions KK of AA and BB a subring of K(t1,…,tn)K(t_1, \ldots, t_n) containing AA and integral over AA. Then BB is a finitely generated AA-module. (Note that the field of fractions of BB is a finite algebraic extension of KK, using Algebra, Chapter V, § 5, no. 7.)

Solution

No solution has been written yet.

Transcribed from the printed volume. Not translated.