We consider the following question of Kunen:
Does Con(ZFC + ∃M a transitive inner model and a non-trivial elementary embedding j: M → V)
imply Con(ZFC + ∃ a measurable cardinal)?
We use core model theory to investigate consequences of the existence of such a j: M → V. We prove, amongst other things, the existence of such an embedding implies that the core model K is a model of “there exists a proper class of almost Ramsey cardinals”. Conversely, if On is Ramsey, then such a j. M are definable.
We construe this as a negative answer to the question above. We consider further the consequences of strengthening the closure assumption on j to having various classes of fixed points.
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