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The logical axioms of identity that sit beneath ZFC: the ground floor everything else is built on.

The axioms of ZFC set theory: the assumptions every definition, lemma and theorem is ultimately proved from.

Every defined term, each built only from the axioms and the definitions before it.

Intermediate results: the scaffolding the larger theorems are assembled from.

Named results, each with a complete proof traceable all the way down to the axioms.