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.
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These labels describe origin, not correctness: citations and verification chips remain separate evidence.
is the ring of rational functions defined at , with maximal ideal generated by and residue field
Example
For a field , This is the ring of rational functions defined at . Its maximal ideal is generated by , and its residue field is canonically .
Facts & Assumptions
Given: A field and the polynomial ring .
Evaluation at is the unique homomorphism fixing and sending to (Universal property of : a coefficient homomorphism and the image of determine a unique ring homomorphism).
For , one has exactly when divides (Factor theorem over a commutative ring).
A quotient by an ideal is a field exactly when the ideal is maximal ( is a field if and only if is a maximal ideal).
Localising at a prime yields a local ring with the extended prime as maximal ideal, and its residue field is the fraction field of the quotient domain ( is local with unique maximal ideal , is the residue field at ).
The rational function field is (For a field , is its rational function field; in particular ).
Every maximal ideal of a commutative ring is prime (Every maximal ideal of a commutative ring is prime).
A homomorphism that sends every denominator to a unit factors uniquely through the localisation (Universal property of localisation: maps that invert factor uniquely through ).
A localisation fraction is zero exactly when some denominator annihilates (Equality, vanishing, and the kernel of the localisation map).
Localisation at a prime ideal uses the multiplicative set (Localisation at a prime ideal: ).
Verification
By [F1] and [F2], evaluation at has kernel and is onto. Explicitly, is well defined and has inverse , so . Thus [F3] makes maximal, and [F6] makes it prime.
By [F9], the denominators are the elements outside , which are exactly the polynomials with by [F2]. They are nonzero and hence units in by [F5], so [F7] gives a map from the localisation to sending to the same fraction. If its image is zero, then because [F5] embeds the domain in its fraction field, and [F8] makes in the localisation. The map is therefore injective, and its image is precisely the displayed fractions, which are exactly those admitting a representative with denominator nonzero at .
By [F4], the maximal ideal is , and the residue field is . Every nonzero denominator in the field is already invertible, so and the last fraction field is canonically .
Depends on
- $R_{\mathfrak p}$ is local with unique maximal ideal $\mathfrak pR_{\mathfrak p}$
- $R_{\mathfrak p}/\mathfrak pR_{\mathfrak p}\cong\operatorname{Frac}(R/\mathfrak p)$ is the residue field at $\mathfrak p$
- Localisation at a prime ideal: $R_{\mathfrak p}=(R\setminus\mathfrak p)^{-1}R$
- $R/M$ is a field if and only if $M$ is a maximal ideal
- Every maximal ideal of a commutative ring is prime
- Universal property of $R[x]$: a coefficient homomorphism and the image of $x$ determine a unique ring homomorphism
- Factor theorem over a commutative ring
- For a field $F$, $F(t)=\operatorname{Frac}(F[t])$ is its rational function field; in particular $\mathbb R(t)=\operatorname{Frac}(\mathbb R[t])$
- Universal property of localisation: maps that invert $S$ factor uniquely through $S^{-1}R$
- Equality, vanishing, and the kernel of the localisation map
Used by
Nothing in the library uses this result yet.
Dependency tree · next 3 levels
Direct dependencies and their dependencies through the next three levels: 65 results over 15 levels. An arrow runs from a result to what uses it, and this result sits at the bottom with a heavier outline. Click the chart to enlarge it.
Sources
- The Stacks Project, Section 10.18: Local rings (standard reference, not scraped)