[Merged by Bors] - chore: notation for (conditional) independence

[RemyDegenne]

Add notations:

• X ⟂ᵢ[μ] Y for independence of X and Y. Simplified to X ⟂ᵢ Y if the measure is volume.
• X ⟂ᵢ[Z, hZ; μ] Y for independence of X and Y given Z. Simplified to X ⟂ᵢ[Z, hZ] Y if the measure is volume.

I don't use a double uptack because neither my browser nor my vscode font have that character (U+2AEB). Instead I have chosen a \perp with an i for indepedence.

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[github-actions]

PR summary 2b8db8b0ae

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

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Declarations diff

No declarations were harmed in the making of this PR! 🐙

You can run this locally as follows

## summary with just the declaration names:
./scripts/declarations_diff.sh <optional_commit>

## more verbose report:
./scripts/declarations_diff.sh long <optional_commit>

The doc-module for script/declarations_diff.sh contains some details about this script.

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No changes to technical debt.

You can run this locally as

./scripts/technical-debt-metrics.sh pr_summary

• The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
• The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).

[grunweg]

Great idea, thank you! I just have a minor comment about discoverability of the notation.
maintainer delegate

[github-actions]

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

[grunweg]

Thanks for adding the comment! How about also mentioning in the doc-strings that the notation is scoped?

[fpvandoorn]

bors d+

[mathlib-bors]

✌️ 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.

[RemyDegenne]

Thanks for the reviews!
bors r+

[mathlib-bors]

Pull request successfully merged into master.

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