feat: hasDetPlusMinusOne_iff_abs_det

[Ruben-VandeVelde]

This seems like a useful characterization.

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[github-actions]

PR summary d9996c5f3e

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

+ hasDetPlusMinusOne_iff_abs_det
+ val_eq_neg_one

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]

Thanks!
bors d+

[grunweg]

Suggested change

	refine ⟨fun h {g} hg => h.abs_det hg, fun h => ⟨?_⟩⟩
	refine ⟨fun h {g} hg ↦ h.abs_det hg, fun h ↦ ⟨?_⟩⟩

[mathlib-bors]

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