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[Merged by Bors] - feat(AlgebraicGeometry): define algebraic cycles#37901

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[Merged by Bors] - feat(AlgebraicGeometry): define algebraic cycles#37901
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Raph-DG:Raph-DG-DefAlgebraicCycle

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@Raph-DG Raph-DG commented Apr 10, 2026

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In this PR we define the notion of algebraic cycles on a scheme, and define the pushforward of an algebraic cycle by a quasicompact morhphism. This was originally defined in #26304, but after some refactoring it was decided that it would be best to split this definition into a separate PR.


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Raph-DG and others added 2 commits June 25, 2026 09:35
Co-authored-by: Christian Merten <christian@merten.dev>
@Raph-DG Raph-DG removed the awaiting-author A reviewer has asked the author a question or requested changes. label Jun 25, 2026
Comment thread Mathlib/AlgebraicGeometry/AlgebraicCycle/Basic.lean
Comment thread Mathlib/AlgebraicGeometry/AlgebraicCycle/Basic.lean Outdated
Raph-DG and others added 2 commits June 25, 2026 11:38
Co-authored-by: Christian Merten <christian@merten.dev>
Co-authored-by: Christian Merten <christian@merten.dev>

@chrisflav chrisflav left a comment

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Thanks!
maintainer merge

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🚀 Pull request has been placed on the maintainer queue by chrisflav.

@mathlib-triage mathlib-triage Bot added the maintainer-merge A reviewer has approved the changed; awaiting maintainer approval. label Jun 25, 2026
@grunweg grunweg changed the title feat(AlgebraicGeometry): Define algebraic cycles feat(AlgebraicGeometry): define algebraic cycles Jun 25, 2026

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Can you add the relevant stack project tags?

Comment thread Mathlib/AlgebraicGeometry/AlgebraicCycle/Basic.lean Outdated
pushforward of a cycle `c` at a point `z = f x`, as in stacks `02R3`.
-/
noncomputable
def mapAux {N : Type*} [DecidableEq N] {Y : Scheme} (f : X ⟶ Y) (wx : X → N) (wy : Y → N) (x : X) :

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Can you make this private?

(see the module docstring for more details).
-/
@[stacks 02QR]
abbrev AlgebraicCycle (X : Scheme.{u}) (R : Type*) [Zero R] :=

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Why is this an abbrev rather than a def? I am not sure but, beside the basic API, I expect that cycles will have their own API.

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It just saves a lot of effort duplicating all of the Function.locallyFinsuppWithin API, and having this as an abbrev hasn't caused problems for me so far. I suppose this is also modelled on the situation in analysis, where divisors are just defined to be terms of type Function.locallyFinsuppWithin (see, e.g. MeromorphicOn.divisor)

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OK, can you maybe add a short comment? I am just afraid of some instance clash at some point, but we can always change if needed. Thanks!

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bors d+

@mathlib-bors mathlib-bors Bot added the delegated This pull request has been delegated to the PR author (or occasionally another non-maintainer). label Jun 25, 2026
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mathlib-bors Bot commented Jun 25, 2026

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✌️ Raph-DG can now approve this pull request until 2026-07-09 12:17 UTC (in 2 weeks). To approve and merge, reply with bors r+. More detailed instructions are available here.

⚠️ This delegation only covers changes within Archive/**, Counterexamples/**, docs/**, DownstreamTest/**, Mathlib/**, MathlibTest/**, widget/**, Archive.lean, Counterexamples.lean, docs.lean, Mathlib.lean; an author commit touching anything else will revoke it. Bors also revokes it if a later push changes too many files for it to check the full list — even if it stays within scope.

@mathlib-triage mathlib-triage Bot removed the maintainer-merge A reviewer has approved the changed; awaiting maintainer approval. label Jun 25, 2026
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Raph-DG commented Jun 25, 2026

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Thanks!

bors r+

@mathlib-bors mathlib-bors Bot added the ready-to-merge This PR has been sent to bors. label Jun 25, 2026
mathlib-bors Bot pushed a commit that referenced this pull request Jun 25, 2026
In this PR we define the notion of algebraic cycles on a scheme, and define the pushforward of an algebraic cycle by a quasicompact morhphism. This was originally defined in #26304, but after some refactoring it was decided that it would be best to split this definition into a separate PR.

Co-authored-by: Raph-DG <raphaeldouglasgiles@gmail.com>
@mathlib-bors mathlib-bors Bot added the bors-staging This PR is currently being built by bors on the staging branch. label Jun 25, 2026
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@mathlib-bors mathlib-bors Bot changed the title feat(AlgebraicGeometry): define algebraic cycles [Merged by Bors] - feat(AlgebraicGeometry): define algebraic cycles Jun 25, 2026
@mathlib-bors mathlib-bors Bot closed this Jun 25, 2026
@mathlib-bors mathlib-bors Bot removed the delegated This pull request has been delegated to the PR author (or occasionally another non-maintainer). label Jun 25, 2026
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