(Weil divisors : Cartier divisors) = (p-Cycles : ? )
(Weil divisors : Cartier divisors) = (p-Cycles : ? )
Suppose
Is there an analogous notion of group of "Cartier
K2-Think
Yes, there is an analogous notion of "Cartier
Key Idea:
For
GPT-5
Short answer: not as a single sheaf. The right higher‑codimension replacement of “Cartier divisors” is no longer captured by global sections of one sheaf; instead one needs a (Gersten) complex of sheaves coming from K‑theory whose last term is the sheaf of codimension‑p cycles.
More precisely (assume X is regular, noetherian; e.g. a smooth variety), set Z^p_X := ⊕{x∈X^{(p)}} i{x,*} Z, the sheaf...
o3 Pro
Let us recall what makes a Cartier divisor different from a Weil divisor.
• A Weil divisor is just a formal linear combination of codimension-1
subvarieties.
• A Cartier divisor, on the other hand, is a subvariety that can be cut out
by ONE equation – i.e. its ideal sheaf is locally generated by a single
non–zero‐divisor. “Locally generated by one element” is what is measured by
the sheaf
...
Claude Opus 4
Yes, there is a notion of higher codimension Cartier cycles, though the theory becomes more subtle and less universally applicable than for divisors. Let me explain the main approaches.
The Analogue: Higher Chow Groups and K-theory
The most direct analogue of Cartier divisors for higher codimension cycles comes from Milnor K-theory and higher Chow groups.
1. Milnor K-sheaves
For...
Gemini 2.5 Pro
This is an excellent and very natural question. The transition from Weil divisors to Cartier divisors is a fundamental step in algebraic geometry, moving from a purely geometric definition (formal sums of subvarieties) to one that is more sheaf-theoretic and tied to local equations. You are asking for the analogous step in higher codimension.
The short answer is: **Yes, such notions exist, but th...
o3
Only in codimension 1 do “Cartier objects’’ behave at all like Weil cycles.
The reason is essentially algebraic: a closed subscheme of
codimension 1 can be described (étale-locally, or even Zariski-locally
if the scheme is integral and normal) by a single non-zero divisor
(i.e. by one equation), and two such local equations differ by a unit.
Therefore the transition functions live in 𝒪×, an ab...
Claude 3.7 Sonnet
Generalizing Cartier Divisors to Higher Codimensions
The question asks about finding a natural generalization of the relationship between Weil divisors and Cartier divisors to higher codimensions.
The Existing Relationship
For codimension 1:
- Weil divisors (Div(X)) are formal sums of codimension 1 subvarieties
- Cartier divisors (Cart(X)) are global sections of $\mathcal{K}_X^{\times}/\ma...
DeepSeek R1
o4 mini
Here is one reasonably concrete way to see that “Cartier‐p–cycles’’ exist exactly by imitating the case p=1, but replacing K₁ by Quillen’s higher K‐theory sheaves. Recall that for p=1 one has on the Zariski site of X the exact sequence of sheaves
0 → 𝒪_X^× → 𝒦_X^× → Cart_X^1 → 0
and by definition Cart^1(X) = Γ(X,Cart_X^1) = coker[Γ(X,𝒪_X^×)→Γ(X,𝒦_X^×)] = principal Weil‐div...
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