[Merged by Bors] - feat(Sym2/Order): s.inf = t.inf ∧ s.sup = t.sup ↔ s = t

[sorrachai]

Characterize equality of two symmetric squares. In a linear order, two symmetric squares are equal if and only if they have the same infimum and supremum.

[github-actions]

PR summary 51fb3db558

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

---

Declarations diff

+ inf_eq_inf_and_sup_eq_sup

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).

[YaelDillies]

The theorem looks useful, thanks! I found a neat golf, so LGTM

maintainer merge

[github-actions]

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

[jcommelin]

Thanks 🎉

bors merge

[mathlib-bors]

Pull request successfully merged into master.

Build succeeded:

• Build
• Lint style