feat(Combinatorics/SimpleGraph/Subgraph): a couple of subgraphOfAdj lemmas

[SnirBroshi]

Also golf a lemma (it's one line longer but it looks simpler to me).

---

[github-actions]

PR summary 6e9770b320

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

---

Declarations diff

+ subgraphOfAdj_adj_self
+ subgraphOfAdj_le_iff

You can run this locally as follows

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

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

The doc-module for scripts/pr_summary/declarations_diff.sh contains some details about this script.

---

No changes to technical debt.

You can run this locally as

./scripts/reporting/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]

Thanks!

maintainer delegate

[YaelDillies]

Maybe grind can golf this even further?

[SnirBroshi]

This is the best I got:

Suggested change

	refine ⟨fun u ↦ ?_, fun v' w' ↦ ?_⟩
	· rintro (rfl | rfl)
	exacts [h.fst_mem, h.snd_mem]
	· rw [subgraphOfAdj_adj, Sym2.eq_iff]
	rintro (⟨rfl, rfl⟩ | ⟨rfl, rfl⟩)
	exacts [h, h.symm]
	constructor
	· grind [subgraphOfAdj_verts, h.fst_mem, h.snd_mem]
	· grind [subgraphOfAdj_adj, h.symm]

Do you prefer it? I'm not sure how robust it is.
If we had some Subgraph.le_iff definitional theorem we might be able to do grind [subgraphOfAdj, H.le_iff, H.edge_vert, h.symm] for the entire theorem (doesn't work for some reason)

[github-actions]

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