How statement and proof provenance work
The first chip identifies the source of the statement or construction; the second identifies the source of its local proof or verification.
- Literature-sourced: the exact statement appears in a cited source; only wording and notation differ.
- AI-adapted: a semantically identical restatement of literature-sourced material, modulo indexing, notation, and boundary cases adopted by the library.
- AI-generated: a genuinely novel statement formulated by AI, with no source for the claim itself.
These labels describe origin, not correctness: citations and verification chips remain separate evidence.
An algebra that is finite dimensional as a vector space over a field is a Noetherian ring
Example
Let be a field and let be a commutative -algebra (Algebras over a commutative ring, central structure maps, and algebra homomorphisms) whose underlying -vector space is finite dimensional, say with (Finite-dimensional vector space, and its dimension ; infinite-dimensional means having no finite basis). Then is a Noetherian ring, and every ideal of is generated by at most elements.
Facts & Assumptions
Given: A field , which is in particular a commutative ring (Every field is a commutative ring with ; it is an integral domain, and it is a commutative division ring), and a commutative -algebra with structure map whose underlying -vector space is finite dimensional of dimension .
An -algebra is a unital ring with a unital ring homomorphism of central image; the induced scalar action makes an -module (Algebras over a commutative ring, central structure maps, and algebra homomorphisms).
A vector space over a field is a set with an addition making an abelian group and a scalar multiplication satisfying , , and (Vector space over a field).
A linear subspace of a vector space over is a subset containing and closed under addition and under scalar multiplication, and it is itself a vector space over under the restricted operations (Linear subspace of a vector space).
is finite-dimensional over when it has a finite basis, and is the unique with a basis satisfying (Finite-dimensional vector space, and its dimension ; infinite-dimensional means having no finite basis).
If is finite dimensional over with and is a linear subspace of , then is finite dimensional over and (If and is a linear subspace of , then is finite-dimensional, , and if and only if ).
A subset is a basis when it is linearly independent and spans (Basis of a vector space: a linearly independent spanning subset; and ordered basis: an injective finite list whose image is a basis).
The span of a subset is the set of its finite linear combinations, and a subset spans when its span is (Linear combination of a finite list, and the span as the smallest linear subspace containing ).
In a commutative ring, consists of finite sums , and (In a commutative ring, consists of finite sums , and ).
For a commutative ring, being Noetherian is equivalent to every ideal being finitely generated (A commutative ring is Noetherian exactly when every ideal is finitely generated, exactly when its ideals satisfy the ascending chain condition, and exactly when every nonempty set of ideals has a maximal member).
An algebra is module-finite over when it is finitely generated as an -module (Subalgebra generated by a subset, algebras of finite type, and module-finite algebras).
A module-finite commutative algebra over a Noetherian commutative ring is a Noetherian ring (A module-finite algebra over a Noetherian ring is a Noetherian ring, and so is every ring between the two).
Every field is a Noetherian ring (Fields and are Noetherian, and so are their polynomial rings in finitely many variables).
Verification
The algebra action makes a -vector space: is an abelian group, and the four displayed scalar identities are exactly the module axioms that the algebra action satisfies. This is the vector-space structure the hypothesis refers to.
Every ideal of is a linear subspace of that vector space: it contains , is closed under addition, and is closed under the scalar action because is a product of an element of with an element of .
By the subspace theorem is finite dimensional over with ; fix a basis of with . Every element of is then a finite -linear combination with .
Hence as an ideal of : each element of equals , which lies in the ideal generated by , and conversely that ideal is contained in because every lies in . So every ideal of is generated by at most elements, and is Noetherian.
The same conclusion follows from the module-finite theorem, and the two agree. A finite basis of generates as a -module, so is module-finite over ; is a Noetherian ring; and a module-finite commutative algebra over a Noetherian ring is Noetherian. The direct argument above is recorded because it also produces the bound on the number of generators, which the general theorem does not.
Remarks
-
Finite dimension over is much stronger than finite type over . A polynomial ring is of finite type over and is Noetherian, but is not finite dimensional as a -vector space; the bound on the number of generators of an ideal disappears there, as the companion false-statement item on this page records for .
-
Commutativity of is assumed only because this page works with commutative rings. The same argument applies verbatim to a left ideal of a finite-dimensional algebra that is not commutative.
Depends on
- A commutative ring is Noetherian exactly when every ideal is finitely generated, exactly when its ideals satisfy the ascending chain condition, and exactly when every nonempty set of ideals has a maximal member
- A module-finite algebra over a Noetherian ring is a Noetherian ring, and so is every ring between the two
- Subalgebra generated by a subset, algebras of finite type, and module-finite algebras
- Finite-dimensional vector space, and its dimension $\dim_F V$; infinite-dimensional means having no finite basis
- If $\dim_F V = n$ and $U$ is a linear subspace of $V$, then $U$ is finite-dimensional, $\dim_F U \le n$, and $\dim_F U = n$ if and only if $U = V$
- Algebras over a commutative ring, central structure maps, and algebra homomorphisms
- Vector space over a field
- Linear subspace of a vector space
- Basis of a vector space: a linearly independent spanning subset; and ordered basis: an injective finite list whose image is a basis
- Linear combination of a finite list, and the span $\operatorname{span}(S)$ as the smallest linear subspace containing $S$
- Every field is a commutative ring with $1 \ne 0$; it is an integral domain, and it is a commutative division ring
- In a commutative ring, $(S)$ consists of finite sums $\sum r_i s_i$, and $(a)=Ra$
- Fields and $\mathbb Z$ are Noetherian, and so are their polynomial rings in finitely many variables
Used by
Nothing in the library uses this result yet.
Dependency tree · two levels
69 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
- A. Altman and S. Kleiman, A Term of Commutative Algebra, 13th ed., Exercise (16.28) (standard reference, not scraped)
- J. S. Milne, A Primer of Commutative Algebra, v4.03, §3 (standard reference, not scraped)