feat(Set): lemmas about set difference

[apnelson1]

We add some API lemmas about set difference and strict subsets.

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[github-actions]

PR summary e12a8f1d46

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

+ _root_.HasSubset.Subset.diff_ssubset_of_nonempty
+ _root_.HasSubset.Subset.ssubset_of_mem_not_mem
+ diff_inter_distrib_right
+ diff_inter_right_comm
+ diff_ssubset_left_iff
+ diff_union_diff_cancel_of_inter_subset_of_subset_union
+ insert_diff_insert
+ inter_diff_right_comm
+ inter_ssubset_left_iff
+ inter_ssubset_right_iff
+ sdiff_lt_left
+ ssubset_union_left_iff
+ ssubset_union_right_iff

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.

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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).

[vihdzp]

Out of curiosity, can any of these be proven by the new tauto_set tactic?

[apnelson1]

Out of curiosity, can any of these be proven by the new tauto_set tactic?

The distributivity ones surely can (though I haven't checked). It doesn't handle nonequality yet, so the ssubset ones can't.

It's too early in the API to actually use the tactic in their proofs, though.

I am already a keen user of the tactic, but I still think these lemmas would be good to have - they are mostly the kind of lemma where rw [show _ by tauto_set] is more cumbersome to write in practice than just rw [lemma_name].