feat(CategoryTheory): right Kan extensions and Guitart exact squares

[joelriou]

This PR only dualises for right Kan extensions what had already been obtained for left Kan extensions.

---

[github-actions]

PR summary a1d55d6dc4

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

---

Declarations diff (regex)

+ IsPointwiseRightKanExtension.compTwoSquare
+ compTwoSquare
+ hasPointwiseRightKanExtension
+ hasPointwiseRightKanExtensionAt_iff
+ hasPointwiseRightKanExtension_iff
+ hasRightKanExtension
+ instance [∀ (F : C₁ ⥤ D), T.HasRightKanExtension F]
+ isIso_ranBaseChange_app
+ isIso_ranBaseChange_app_iff
+ isPointwiseRightKanExtensionAtCompTwoSquareEquiv
+ isPointwiseRightKanExtensionEquivOfGuitartExact
+ isPointwiseRightKanExtensionOfCompTwoSquare
+ nonempty_isPointwiseRightKanExtensionAt_compTwoSquare_iff
+ ranBaseChange

You can run this locally as follows

## from your `mathlib4` directory:
git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci

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

## more verbose report:
../mathlib-ci/scripts/pr_summary/declarations_diff.sh long <optional_commit>

The doc-module for scripts/pr_summary/declarations_diff.sh in the mathlib-ci repository contains some details about this script.

Declarations diff (Lean)

✅ Lean-aware diff — post-build, computed from the Lean environment (commit a1d55d6).

• +15 new declarations
• −0 removed declarations

+CategoryTheory.Functor.RightExtension.IsPointwiseRightKanExtension.compTwoSquare
+CategoryTheory.Functor.RightExtension.compTwoSquare
+CategoryTheory.Functor.RightExtension.isPointwiseRightKanExtensionAtCompTwoSquareEquiv
+CategoryTheory.Functor.RightExtension.isPointwiseRightKanExtensionEquivOfGuitartExact
+CategoryTheory.Functor.RightExtension.isPointwiseRightKanExtensionOfCompTwoSquare
+CategoryTheory.Functor.RightExtension.nonempty_isPointwiseRightKanExtensionAt_compTwoSquare_iff
+CategoryTheory.TwoSquare.hasPointwiseRightKanExtension
+CategoryTheory.TwoSquare.hasPointwiseRightKanExtensionAt_iff
+CategoryTheory.TwoSquare.hasPointwiseRightKanExtension_iff
+CategoryTheory.TwoSquare.hasRightKanExtension
+CategoryTheory.TwoSquare.instIsIsoFunctorRanBaseChangeOfGuitartExact
+CategoryTheory.TwoSquare.isIso_ranBaseChange_app
+CategoryTheory.TwoSquare.isIso_ranBaseChange_app_iff
+CategoryTheory.TwoSquare.ranBaseChange
+CategoryTheory.TwoSquare.ranBaseChange_app

---

Increase in strong tech debt: (relative, absolute) = (0.26, 0.00)

Current number	Change	Type (strong)
backward.defeqAttrib.useBackward	4305	-1
backward.isDefEq.respectTransparency.types	2506	1

No changes to weak technical debt.

Current commit a1d55d6dc4
Reference commit bbcd1968ee

This script lives in the mathlib-ci repository. To run it locally, from your mathlib4 directory:

git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci
../mathlib-ci/scripts/reporting/technical-debt-metrics.py 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).

[github-actions]

✅ PR Title Formatted Correctly

The title of this PR has been updated to match our commit style conventions.
Thank you!

[robin-carlier]

Thanks! Can you also remove the unnecessary set_options in the left Kan extensions portion of the file as well?

maintainer delegate

[github-actions]

🚀 Pull request has been placed on the maintainer queue by robin-carlier.