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Every commutative Artinian ring is Noetherian
Statement
Assume the Axiom of Choice.
Let be a commutative Artinian ring. Then is Noetherian.
Facts & Assumptions
Given: A commutative Artinian ring and the Axiom of Choice.
Proof
Let . By An Artinian ring has only finitely many maximal ideals, the maximal ideals of are for some unless , in which case the conclusion is immediate. By The nilradical is the intersection of all prime ideals and Every prime ideal of an Artinian ring is maximal, one has . Distinct maximal ideals are comaximal, so Chinese remainder theorem for pairwise comaximal ideals gives . Each factor is a field by is a field if and only if is a maximal ideal, and a field is Noetherian because its only ideals are and itself. Repeated use of A product of two Noetherian rings is Noetherian therefore shows that is Noetherian.
By The nilradical of an Artinian ring is a nilpotent ideal, choose with . For each , put . Because , the action of on factors through , so is a -module. Transport the standard idempotents of the product ring in step 1.1 to elements . Then , and each summand is naturally a vector space over the field . If some had no finite spanning set, recursively choose with ; then would be a strict descending chain of -submodules of . But submodules of correspond to submodules of the ideal containing , so this would give a strict descending chain of ideals in the Artinian ring , impossible. Hence every has a finite basis, and is finitely generated as a -module.
Since is Noetherian, Finitely generated modules over a left Noetherian ring are Noetherian shows that each is Noetherian as a -module, hence as an -module. The filtration has successive quotients and , all Noetherian. Repeatedly applying Noetherian and Artinian conditions are each exact in short exact sequences to the short exact sequences shows that the regular module is Noetherian. Therefore Left and right Noetherian rings makes a Noetherian ring.
Depends on
- Left and right Noetherian rings
- Every prime ideal of an Artinian ring is maximal
- An Artinian ring has only finitely many maximal ideals
- The nilradical of an Artinian ring is a nilpotent ideal
- The nilradical is the intersection of all prime ideals
- Chinese remainder theorem for pairwise comaximal ideals
- $R/M$ is a field if and only if $M$ is a maximal ideal
- A product of two Noetherian rings is Noetherian
- Finitely generated modules over a left Noetherian ring are Noetherian
- Noetherian and Artinian conditions are each exact in short exact sequences
Used by
Dependency tree · two levels
40 results within two dependency steps of this one, each drawn at its shortest distance from it. An arrow runs from a result to what uses it, so the chart reads left to right and ends at this result, which carries a heavier outline. Every node is a link to that result. Click elsewhere on the chart to enlarge it.
Sources
- J. S. Milne, A Primer of Commutative Algebra, v4.03, Theorem 16.6 (standard reference, not scraped)
- The Stacks Project, Section 10.53: Artinian rings (standard reference, not scraped)