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15
votes
Accepted
Does stationary reflection imply Mahloness?
Not necessarily. Here's a counterexample, but I'm sure it is a ridiculous overkill in consistency strength:
Suppose $\kappa$ is the least inaccessible limit of supercompact cardinals. Then $\kappa$ …
14
votes
Why believe in the existence of large cardinals rather than just their consistency?
I think it can be reasonably argued that the large cardinal notions follow a common conceptual pattern, even a semi-formal template. Once we understood the characterization of measurable cardinals in …
12
votes
Accepted
What is the evidence for and against the HOD conjecture?
I believe it is fair to say that the HOD Conjecture has been refuted.
The HOD Conjecture is the statement that the theory ZFC + "There is an extendible cardinal" proves that there is a proper class of …
11
votes
Accepted
A question regarding the relation between Freiling's Axiom of Symmetry and real-valued measu...
Real-valued measurable cardinals (RVM) are equiconsistent with 2-valued measurable cardinals. I believe this is due to Solovay and Kunen. (Solovay for the forcing direction, Kunen for the inner mode …
9
votes
Accepted
Why isn't there more interest in "large powerset axioms"?
I suppose there is some interest in propositions implying large powerset. For example, a classical question at the infancy of set theory and real analysis was whether there is a probability measure on …
7
votes
capturing small sets in small factors
We now have a full answer. The capturing property is equivalent to weak compactness.
Yair already covered the non-inaccessible case. Now we show that this property implies the tree property at $\ka …
7
votes
Accepted
"Potentially club" filters on $\omega_2$
First, your notation is nonstandard; when we write $\mathrm{Col}(\kappa,\lambda)$, this typically means the set of partial functions $p : \kappa \to \lambda$ of size $<\kappa$, i.e. reverse of yours.
…
7
votes
Can we have a $\kappa$-Suslin tree where $\kappa$ is above a measurable cardinal?
To complement Joel's answer and tie into the issue of $L$, consider a model $L[U]$, where $U$ is a normal measure on a cardinal $\kappa$. It is well-known that $L[U]$ satisfies GCH and $\diamondsuit_ …
6
votes
Reference for proof that consistency of $\omega_1$-Erdos cardinal implies Con(Chang's Conjec...
A sketch of Silver's original argument appears in section 19 here: http://math.bu.edu/people/aki/e.pdf
6
votes
PFA: A New Godel's Program & A New Large Cardinal Ladder (Updated)
If we start with an indestructibly supercompact cardinal $\kappa$, then we can do Easton forcing to get any reasonable continuum function on the regular cardinals $\geq \kappa$ and retain the supercom …
6
votes
Accepted
Large cardinals and measurability in $L(A)$
For each $\alpha<\omega_1$, choose a real $r_\alpha$ that codes the ordertype $\alpha$. This sequence $\langle r_\alpha : \alpha < \omega_1 \rangle$ then codes a sequence of surjections from $\omega$ …
6
votes
What is known about the least cardinal where $\kappa$ fails to be supercompact?
I'm not sure if this gets to the heart of the question, but here are some observations.
For a successor ordinal $\alpha$, let $\kappa_\alpha$ be the least $\kappa>\alpha$ which is $\kappa^{+\alpha}$-s …
6
votes
Collapsing the cardinals between two singular cardinals
For question 2, some large cardinals imply the existence of such a forcing. Suppose $\kappa$ is 2-huge, with $j : V \to M$ an elementary embedding, $\lambda = j(\kappa)$, $\theta = j(\lambda)$, and $ …
6
votes
Accepted
Forcing $\neg\square_{\omega_1}$ from a Mahlo cardinal, reference
I'll give the proof, which was told to me by Martin Zeman.
Let $G \subseteq \mathrm{Col}(\omega_1,{<}\kappa)$ be generic, where $\kappa$ is Mahlo. Suppose towards contradiction that $\square_{\omega_ …
5
votes
Accepted
Definition of ineffability behind reflection principles in set theory
Referring to proper classes by means of constants clearly doesn’t use the “internal properties” of the universe of sets. You’re literally reaching outside the universe and adding an artificial means …