Bourbaki

Exercise 7, § 4

Commutative Algebra, IX

Let A be a Krull ring and P the set of its prime ideals of height 1. Suppose that for every prime ideal p∈Pp \in P, the ring A/pA/p is noetherian, and denote by K the field of fractions of A. Prove that A is noetherian. (Let p∈Pp \in P and x∈Kx \in K be such that vp(x)=1v_p(x) = 1 and vq(x)≤0v_q(x) \leq 0 for q∈P−{p}q \in P - \{p\}. Put B=A[x]B = A[x]. Then one has the following properties: (i) p=xB∩Ap = xB \cap A; (ii) the inclusion of A in B induces, by passing to quotients, an isomorphism of A/pA/p onto B/xBB/xB; (iii) for every integer n≥0n \geq 0, the ring B/xnBB/x^nB is noetherian ; (iv) for every integer n≥0n \geq 0, the ring A/(xnB∩A)A/(x^nB \cap A) is noetherian (use Exercise 6); (v) for every integer n≥0n \geq 0, the A-module A/p(n)A/p^{(n)} is noetherian. Recall that one puts p(n)=A∩pnApp^{(n)} = A \cap p^nA_p, cf. IV, § 2, Exercise 18.)

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