[Merged by Bors] - feat(Algebra/Homology): exact sequences with four terms

[joelriou]

The main definition in this file is ComposableArrows.Exact.cokerIsoKer: given an exact sequence S (involving at least four objects), this is the isomorphism from the cokernel of S.map' k (k + 1) to the kernel of S.map' (k + 2) (k + 3).

This will be used in the formalization of spectral sequences #33842.

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[github-actions]

PR summary 28323863fa

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference
Mathlib.Algebra.Homology.ExactSequenceFour (new file)	738

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Declarations diff

+ Exact.sc
+ Exact.sc'
+ cokerIsoKer
+ cokerIsoKer'
+ cokerIsoKer'_hom_inv_id
+ cokerIsoKer'_inv_hom_id
+ cokerIsoKer_hom_fac
+ cokerToKer
+ cokerToKer'_fac
+ cokerToKer_fac
+ epi_cokerToKer'
+ isIso_cokerToKer'
+ mono_cokerToKer'
+ opcyclesIsoCycles
+ opcyclesIsoCycles_hom_fac
+ opcyclesToCycles
+ opcyclesToCycles_fac
++ cokerToKer'

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).

[dagurtomas]

Thanks!

maintainer delegate

[github-actions]

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

[jcommelin]

Thanks 🎉

bors merge

[mathlib-bors]

Pull request successfully merged into master.

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