[Merged by Bors] - feat(QuotientGroup): surjectivity and kernel of QuotientGroup.map

[xroblot]

Prove formulas for the kernel of QuotientGroup.lift and QuotientGroup.map and that these maps are surjective if the corresponding functions are surjective.

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• depends on: [Merged by Bors] - feat(GroupTheory/Congruences): add the equiv between congruence relations on a group and its normal subgroup #23269

[github-actions]

PR summary 652a2ba699

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

+ Quotient.lift_surjective
+ Quotient.lift_surjective_iff
+ ker_lift
+ ker_map
+ ker_toSubmonoid
+ lift_comp_mk'
+ lift_surjective_of_surjective
+ map_comap_eq_self_of_surjective
+ map_surjective_of_surjective
+ map_toSubmonoid

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.

---

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).

[mathlib4-dependent-issues-bot]

This PR/issue depends on:

• [Merged by Bors] - feat(GroupTheory/Congruences): add the equiv between congruence relations on a group and its normal subgroup #23269
  By Dependent Issues (🤖). Happy coding!

[urkud]

Thanks! Once you address these comments, please tag me, and I'll try to quickly review&merge the new version.

[xroblot]

@urkud The new version is ready for your review. Thanks!

[urkud]

Thanks!
bors d+

[mathlib-bors]

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

[xroblot]

bors r+

[mathlib-bors]

Pull request successfully merged into master.

Build succeeded:

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