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If is Noetherian then is Noetherian for every
Statement
Let be a Noetherian commutative ring. Then the iterated polynomial ring of Polynomial rings in finitely many commuting indeterminates by iteration is Noetherian for every .
The index starts at , where the published definition sets and the assertion is the hypothesis itself.
Facts & Assumptions
Given: A Noetherian commutative ring .
Polynomial rings in finitely many commuting indeterminates are defined recursively by and (Polynomial rings in finitely many commuting indeterminates by iteration).
If is a Noetherian commutative ring then is a Noetherian commutative ring (Hilbert basis theorem: if is Noetherian then is Noetherian).
Proof
At the recursive definition gives , which is Noetherian by hypothesis; this is the base of the induction and is not skipped.
Let and assume is Noetherian.
The recursive definition gives , a polynomial ring in one indeterminate over the ring assumed Noetherian in step 1.2; the Hilbert basis theorem applied to that ring makes Noetherian.
The base case of step 1.1 and the passage of step 2.1 give, by induction on , that is Noetherian for every .
Remarks
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Finitely many indeterminates is essential. The induction produces a proof for each separately and says nothing about a ring of polynomials in infinitely many indeterminates; the companion examples page carries a witness that the conclusion fails there.
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The converse holds too, by iterating is Noetherian if and only if is Noetherian down the tower of coefficient rings.
Depends on
Used by
- A plane intersection with no common component is nonempty and zero-dimensional Corollary
- Every algebra of finite type over a Noetherian ring is a Noetherian ring Corollary
- Every algebra of finite type over a Noetherian ring is finitely presented Corollary
- A cusp family defeats the missing source hypothesis Counterexample
- Ramification points, branch points and unramifiedness Definition
- The intrinsic Zariski tangent space Definition
- The normalized Khovanov-Rozansky HOMFLYPT Euler series Definition
- A nonfree maximal Cohen--Macaulay module Example
- A parameter sequence regular in a hypersurface Example
- All twists on the projective line Example
- An upper jump of h0 in a flat projective family Example
- Fields and ℤ are Noetherian, and so are their polynomial rings in finitely many variables Example
- Localizing (x²,xy)=(x)∩(x,y)² keeps only the matching component Example
- The subalgebra k[x,xy,xy²,…] of k[x,y] is not Noetherian Example
- Two minimal decompositions of (x²,xy) share radicals but not the embedded component Example
- ℤ and k[x] are Noetherian but not Artinian Example
- False statement: in a Noetherian ring there is a single bound on the number of generators an ideal needs False statement
- A classical affine algebraic set has a unique finite irredundant decomposition Lemma
- An S-rational map defined after a faithfully flat smooth base change is defined Lemma
- Embedded flat deformations of a smooth hypersurface are deformations of its equation Lemma
- Finite local length exactly when no common local branch Lemma
- Finite twisted locally free resolutions on projective space Lemma
- Finite-type field extensions with zero Ω Lemma
- Generic freeness over a Noetherian domain Lemma
- High-degree section module is finite graded Lemma
- Over a Noetherian ring, an ideal filtration is stable exactly when its Rees module is finite, and the Rees algebra is Noetherian Lemma
- Standard smooth algebras are finitely presented and flat Lemma
- The blowup of a one-dimensional integral Noetherian scheme at a closed point is finite Lemma
- The Laurent polynomial ring is Noetherian and a unique factorisation domain Lemma
- The product of two projective lines is an integral smooth projective surface Lemma
- Which constructions preserve the Noetherian condition, and which do not Remark
- A finite graded module over a standard graded algebra has rational Hilbert series and eventual polynomial growth Theorem
- Completion of a Noetherian ring is Noetherian Theorem
- Degree of the coherent Hilbert polynomial Theorem
- Euler characteristic is a Hilbert polynomial Theorem
- localisation and polynomial extension of regular rings Theorem
- Serre vanishing for coherent sheaves and ample twists Theorem
- The dimension formula for affine domains Theorem
Dependency tree · two levels
6 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
- B. Totaro, Commutative Algebra (Michaelmas 2011), notes by Z. Norwood, §8 Corollary 8.4 (standard reference, not scraped)
- A. Altman and S. Kleiman, A Term of Commutative Algebra, 13th ed., (16.12) (standard reference, not scraped)