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[Merged by Bors] - feat(probability/upcrossing): Doob's upcrossing estimate #14933

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khwilson pushed a commit that referenced this pull request Aug 2, 2022
…rty of the conditional expectation (#15274)

We prove this result:
```lean
lemma condexp_strongly_measurable_mul {f g : α → ℝ} (hf : strongly_measurable[m] f)
  (hfg : integrable (f * g) μ) (hg : integrable g μ) :
  μ[f * g | m] =ᵐ[μ] f * μ[g | m] :=
```
This could be extended beyond multiplication, to any bounded bilinear map, but we leave this to a future PR. For now we only prove the real multiplication case, which is needed for #14909 and #14933.
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This looks very good, thanks!

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namespace measure_theory

variables {α ι : Type*} {m0 : measurable_space α} {μ : measure α}
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Is there a reason you call the space α and not Ω, and your measure μ and not (and the points in the space x and not ω)? I know it doesn't make any difference, but it can help your probability-inclined reader.

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@JasonKYi JasonKYi Aug 6, 2022

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I've changed α to Ω and x to ω. I've not switched μ to since this file had opened probability.notation and it seems the notation for being the volume doesn't allow me to declare it as a measure (I can't use measure_space here since I want to specify the measurable_space).

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@sgouezel sgouezel added awaiting-author A reviewer has asked the author a question or requested changes and removed awaiting-review The author would like community review of the PR labels Aug 6, 2022
@JasonKYi JasonKYi 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 Aug 6, 2022
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sgouezel commented Aug 7, 2022

bors r+
Thanks!

@github-actions github-actions bot added ready-to-merge All that is left is for bors to build and merge this PR. (Remember you need to say `bors r+`.) and removed awaiting-review The author would like community review of the PR labels Aug 7, 2022
bors bot pushed a commit that referenced this pull request Aug 7, 2022
This PR proves Doob's upcrossing estimate which is central for the martingale convergence theorems.



Co-authored-by: RemyDegenne <Remydegenne@gmail.com>
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bors bot commented Aug 7, 2022

Pull request successfully merged into master.

Build succeeded:

@bors bors bot changed the title feat(probability/upcrossing): Doob's upcrossing estimate [Merged by Bors] - feat(probability/upcrossing): Doob's upcrossing estimate Aug 7, 2022
@bors bors bot closed this Aug 7, 2022
@bors bors bot deleted the JasonKYi/upcrossing_new branch August 7, 2022 08:26
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