feat(Combinatorics): a clique has size at most the chromatic number

[YaelDillies]

There already exists a version of this lemma for cliques given by a set, but it's impractical to provide an explicit clique on an explicit graph as a set, rather than an indexed family, especially because computing the size of the set would then involve proving that it is the range of an injective function, even though being a clique already implies being injective!

Application: google-deepmind/formal-conjectures#1369

From FormalConjectures

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[github-actions]

PR summary ba422618a7

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

+ Colorable.card_le_of_pairwise_adj
+ Coloring.injective_comp_of_pairwise_adj
+ isSymm_adj
+ le_chromaticNumber_iff_colorable
+ le_chromaticNumber_iff_coloring
+ le_chromaticNumber_of_pairwise_adj

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).