refactoring Matroid ext lemmas

[madvorak]

---

Please doublecheck whether I used @[ext] correctly.

[github-actions]

PR summary d58d4a9eea

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

---

Declarations diff

+ ext_base
+ ext_iff_base
+ ext_iff_indep
+ ext_indep
- eq_iff_indep_iff_indep_forall
- eq_of_base_iff_base_forall
- eq_of_indep_iff_indep_forall

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).

[apnelson1]

LGTM

[apnelson1]

Perhaps ∀ ⦃I⦄, I ⊆ M.E → _ instead (and also in the iff version)? To match with ext_base.

[apnelson1]

Maybe add an iff version too:

theorem ext_iff_base {M₁ M₂ : Matroid α} :
    M₁ = M₂ ↔ M₁.E = M₂.E ∧ ∀ ⦃B⦄, B ⊆ M₁.E → (M₁.Base B ↔ M₂.Base B) :=
  ⟨fun h ↦ by simp [h], fun ⟨hE, h⟩ ↦ ext_base hE h⟩