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[Merged by Bors] - feat(Probability/Kernel): disintegration of finite kernels #10603

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@RemyDegenne RemyDegenne commented Feb 15, 2024

Let κ : kernel α (β × Ω) be a finite kernel, where Ω is a standard Borel space. Then if α is countable or β has a countably generated σ-algebra (for example if it is standard Borel), then there exists a kernel (α × β) Ω called conditional kernel and denoted by condKernel κ such that κ = fst κ ⊗ₖ condKernel κ.

Properties of integrals involving condKernel are collated in the file Integral.lean.
The conditional kernel is unique (almost everywhere w.r.t. fst κ): this is proved in the file Unique.lean.


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@RemyDegenne RemyDegenne added WIP Work in progress t-measure-probability Measure theory / Probability theory labels Feb 15, 2024
@RemyDegenne RemyDegenne added awaiting-review The author would like community review of the PR and removed awaiting-author A reviewer has asked the author a question or requested changes labels Apr 7, 2024
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The refactor is done and this is ready for review. The PR is big, but if I dismantle the old disintegration file I have to have all the replacements in the PR (which means I can't PR the files about integrals and uniqueness later).

@leanprover-community-mathlib4-bot leanprover-community-mathlib4-bot added the merge-conflict The PR has a merge conflict with master, and needs manual merging. label Apr 11, 2024
@leanprover-community-mathlib4-bot leanprover-community-mathlib4-bot added merge-conflict The PR has a merge conflict with master, and needs manual merging. and removed merge-conflict The PR has a merge conflict with master, and needs manual merging. labels Apr 12, 2024
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This looks great, thanks! Sorry for the delay to review the PR (it means there is another merge conflict that you have to solve...)
bors d+

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This theorem in the case of finite kernels is weaker than `eq_condKernel_of_measure_eq_compProd`
which asserts that the kernels are equal almost everywhere and not just on a given measurable
set. -/
theorem eq_condKernel_of_measure_eq_compProd' (κ : kernel α Ω) [IsSFiniteKernel κ]
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I think I am unhappy with the assumptions in this theorem and in the next ones: if ρ = ρ.fst ⊗ₘ κ and ρ is a finite measure, then κ a should have finite mass almost everywhere wrt ρ.fst, and I feel that this should be sufficient to carry out the arguments in the lemma without the assumptions of s-finiteness or of finiteness. However, the lemmas were already there (at least in the measure version) and you just copied them, so this shouldn't hold the PR back. I'll investigate that once this one is merged, if you agree.

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mathlib-bors bot commented Apr 16, 2024

✌️ RemyDegenne can now approve this pull request. To approve and merge a pull request, simply reply with bors r+. More detailed instructions are available here.

@leanprover-community-mathlib4-bot leanprover-community-mathlib4-bot removed the merge-conflict The PR has a merge conflict with master, and needs manual merging. label Apr 16, 2024
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Thanks for all the reviews and for your help on the disintegration PRs. No worries about the review time: I don't expect a quick review for a 1000 lines PR :)
I agree that the assumptions in the Unique file don't feel right. I won't work on that myself for now (at least not for the next days), so feel free to have a look.

bors r+

@github-actions github-actions bot added the ready-to-merge This PR has been sent to bors. label Apr 16, 2024
mathlib-bors bot pushed a commit that referenced this pull request Apr 16, 2024
Let `κ : kernel α (β × Ω)` be a finite kernel, where `Ω` is a standard Borel space. Then if `α` is countable or `β` has a countably generated σ-algebra (for example if it is standard Borel), then there exists a `kernel (α × β) Ω` called conditional kernel and denoted by `condKernel κ` such that `κ = fst κ ⊗ₖ condKernel κ`.

Properties of integrals involving `condKernel` are collated in the file `Integral.lean`.
The conditional kernel is unique (almost everywhere w.r.t. `fst κ`): this is proved in the file `Unique.lean`.




Co-authored-by: sgouezel <sebastien.gouezel@univ-rennes1.fr>
Co-authored-by: Rémy Degenne <remydegenne@gmail.com>
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mathlib-bors bot commented Apr 16, 2024

Pull request successfully merged into master.

Build succeeded:

@mathlib-bors mathlib-bors bot changed the title feat(Probability/Kernel): disintegration of finite kernels [Merged by Bors] - feat(Probability/Kernel): disintegration of finite kernels Apr 16, 2024
@mathlib-bors mathlib-bors bot closed this Apr 16, 2024
@mathlib-bors mathlib-bors bot deleted the RD_disintegration branch April 16, 2024 13:20
atarnoam pushed a commit that referenced this pull request Apr 16, 2024
Let `κ : kernel α (β × Ω)` be a finite kernel, where `Ω` is a standard Borel space. Then if `α` is countable or `β` has a countably generated σ-algebra (for example if it is standard Borel), then there exists a `kernel (α × β) Ω` called conditional kernel and denoted by `condKernel κ` such that `κ = fst κ ⊗ₖ condKernel κ`.

Properties of integrals involving `condKernel` are collated in the file `Integral.lean`.
The conditional kernel is unique (almost everywhere w.r.t. `fst κ`): this is proved in the file `Unique.lean`.




Co-authored-by: sgouezel <sebastien.gouezel@univ-rennes1.fr>
Co-authored-by: Rémy Degenne <remydegenne@gmail.com>
uniwuni pushed a commit that referenced this pull request Apr 19, 2024
Let `κ : kernel α (β × Ω)` be a finite kernel, where `Ω` is a standard Borel space. Then if `α` is countable or `β` has a countably generated σ-algebra (for example if it is standard Borel), then there exists a `kernel (α × β) Ω` called conditional kernel and denoted by `condKernel κ` such that `κ = fst κ ⊗ₖ condKernel κ`.

Properties of integrals involving `condKernel` are collated in the file `Integral.lean`.
The conditional kernel is unique (almost everywhere w.r.t. `fst κ`): this is proved in the file `Unique.lean`.




Co-authored-by: sgouezel <sebastien.gouezel@univ-rennes1.fr>
Co-authored-by: Rémy Degenne <remydegenne@gmail.com>
callesonne pushed a commit that referenced this pull request Apr 22, 2024
Let `κ : kernel α (β × Ω)` be a finite kernel, where `Ω` is a standard Borel space. Then if `α` is countable or `β` has a countably generated σ-algebra (for example if it is standard Borel), then there exists a `kernel (α × β) Ω` called conditional kernel and denoted by `condKernel κ` such that `κ = fst κ ⊗ₖ condKernel κ`.

Properties of integrals involving `condKernel` are collated in the file `Integral.lean`.
The conditional kernel is unique (almost everywhere w.r.t. `fst κ`): this is proved in the file `Unique.lean`.




Co-authored-by: sgouezel <sebastien.gouezel@univ-rennes1.fr>
Co-authored-by: Rémy Degenne <remydegenne@gmail.com>
Jun2M pushed a commit that referenced this pull request Apr 24, 2024
Let `κ : kernel α (β × Ω)` be a finite kernel, where `Ω` is a standard Borel space. Then if `α` is countable or `β` has a countably generated σ-algebra (for example if it is standard Borel), then there exists a `kernel (α × β) Ω` called conditional kernel and denoted by `condKernel κ` such that `κ = fst κ ⊗ₖ condKernel κ`.

Properties of integrals involving `condKernel` are collated in the file `Integral.lean`.
The conditional kernel is unique (almost everywhere w.r.t. `fst κ`): this is proved in the file `Unique.lean`.




Co-authored-by: sgouezel <sebastien.gouezel@univ-rennes1.fr>
Co-authored-by: Rémy Degenne <remydegenne@gmail.com>
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