The problem of finding the ultimate core model, one that contains all large cardinals.
If ℵω is a strong limit cardinal, then 2ℵω < ℵω1 (see Singular cardinals hypothesis). The best bound, ℵω4, was obtained by Shelah using his pcf theory.
Woodin's Ω-hypothesis.
Does the consistency of the existence of a strongly compact cardinal imply the consistent existence of a supercompact cardinal?
(Woodin) Does the Generalized Continuum Hypothesis below a strongly compact cardinal imply the Generalized Continuum Hypothesis everywhere?
Does there exist a Jónsson algebra on ℵω?
Without assuming the axiom of choice, can a nontrivial elementary embedding V→V exist?

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