Worldly cardinals below an inaccessible cardinal
ID: worldly-cardinals-below-an-inaccessible-cardinal
Below any uncountable strongly inaccessible cardinal , the worldly cardinals contain a closed unbounded subset of and hence have cardinality . The structure models ZFC. Reflect each finite group from an enumeration of all first-order formulas to a closed unbounded subset of , using and regularity for the witness bounds. The countable intersection remains closed unbounded, so its ranks are elementary substructures of . Intersect with the closed unbounded subset of infinite cardinal numbers below . Uncountability is essential: the regular strong limit has no worldly cardinal below it.
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