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8 votes
Accepted

Mahlo cardinal and hyper k-inaccessible cardinal

The answer is no. Mahloness is much stronger than this. Every Mahlo cardinal $\kappa$ is a limit of such cardinals. One can see this, because there is a club of $\gamma<\kappa$ with $V_\gamma\prec V …
Joel David Hamkins's user avatar
7 votes
Accepted

Do strong embeddings always provide all the ultrafilters that exist?

If all we want is that for every measure $U$ there is a strongness embedding with a seed for $U$, then the answer is yes. To see this, suppose $\kappa$ is a strong cardinal, and let $U$ be any $\kappa …
Joel David Hamkins's user avatar
12 votes
Accepted

A question about "local" versus "global" large cardinal axioms

I don't agree that it is difficult to formalize the local/global distinction, and indeed, I think that there is a largely agreed-upon technical meaning for these notions. Specifically, a property is …
Joel David Hamkins's user avatar
11 votes
Accepted

Is there a large-cardinal completeness theorem for $L$?

On the one hand, we cannot easily describe any such list of axioms, since if $\Lambda$ was computably enumerable, then by your third bullet point, the arithmetic consequences of ZFC+(V=L)+$\Lambda$ wo …
Joel David Hamkins's user avatar
5 votes
Accepted

Covering properties of strongly compact embedding

This is a very nice question (and indeed, I remember asking myself this question when I was a graduate student). The answer in general is that no, you do not get any extra strength from having these …
Joel David Hamkins's user avatar
4 votes
Accepted

Elementary embeddings with the same critical point

Yes, this situation can occur. One should simply undertake the dual of the construction you had suggested with iterated ultrapowers. Specifically, suppose that $\mu$ is a normal measure on a measura …
Joel David Hamkins's user avatar
7 votes
Accepted

Is there a simple combinatorial characterization for when a direct limit of ultrapowers of $...

The answer is yes. Theorem. The direct limit ultrapower you describe is well-founded if and only if $\bigcap_n A_n\neq \emptyset$ whenever $A_n\in U$ for all $n$. Proof. You've already noted the con …
Joel David Hamkins's user avatar
5 votes
Accepted

$\text{ZFGC}^{\text{−f}}+\text{BAFA}+\exists\kappa(κ \text{ is Reinhardt})$ and its implication

I'm glad to hear you're reading our paper, which can be found here: The foundation axiom and elementary self-embeddings of the universe. Click through to the arxiv for a pdf — and I note that the titl …
Joel David Hamkins's user avatar
8 votes

Increasing and Descending Chains of Inner Models for Measurable Cardinals

I assume that by $M_{\kappa,\mu}$ you intend the ultrapower of $V$ by $\mu$. Both of the statements are inconsistent, even in the case of only two measurable cardinals, let alone a proper class of t …
Joel David Hamkins's user avatar
7 votes
Accepted

If $\kappa$ is weakly inaccessible, then is it the $\kappa$-th aleph fixed point

If $\kappa$ is weakly inaccessible, then it is a limit cardinal and hence $\kappa=\aleph_\lambda$ for some limit ordinal $\lambda$. Since the cofinality of $\aleph_\lambda$ is the same as the cofinali …
Joel David Hamkins's user avatar
8 votes
Accepted

Applications of higher-order reflection principles

I view these kinds of hypotheses as on a continuum stretching from weak compactness up through all the levels of the indescribability hierarchy, second order, third order and so on. This hierarchy of …
Joel David Hamkins's user avatar
10 votes
Accepted

The Kunen inconsistency and definable classes

My perspective on this issue is that there are a variety of ways to take the claim of the Kunen inconsistency, and we needn't pick a particular one as the only right one. Rather, we gain a fuller pers …
Joel David Hamkins's user avatar
4 votes

A question about supercompact cardinal numbers

No, this is not possible. If κ is supercompact, then in particular it is measurable, and there is a normal measure μ on κ that concentrates on non-measurable cardinals. If j:V to M is the correspond …
Joel David Hamkins's user avatar
8 votes
Accepted

Strong Cardinals and Supercompact Cardinals

In general, $\lambda$-supercompactness, if consistent, does not imply $\lambda$-strongness. One can see this by observing that the smallest cardinal $\kappa$ that is $\kappa^+$-supercompact is never $ …
Joel David Hamkins's user avatar
4 votes
Accepted

Ultrapowers by normalized ultrafilters

I would answer question 1 by saying that $M=\text{Ult}(V,U)$ if and only if $j$ is isomorphic to an ultrapower by some normal measure. This is another way of saying that normal measures are minimal wi …
Joel David Hamkins's user avatar

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