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This tag is used if a reference is needed in a paper or textbook on a specific result.
4
votes
Accepted
Disjoint refinements in $P(\kappa)/J$
In my thesis I proved that my conjecture is false. It's not so simple-- the proof ties together chapter 2 and sections 5.1, 5.2, and 6.3.
7
votes
1
answer
385
views
$\aleph_2$ Suslin Hypothesis
Is it still open whether ZFC+GCH is consistent with the statement that there are no $\aleph_2$-Suslin trees?
3
votes
1
answer
170
views
Disjoint refinements in $P(\kappa)/J$
The following is a theorem of Baumgartner, Hajnal, and Mate:
Suppose $J$ is a normal ideal on $\omega_1$ which is nowhere $\omega_1$-dense. Then for any sequence $\langle A_\alpha : \alpha < \omega_ …
3
votes
0
answers
127
views
Is there a name for this operation on integer functions?
Suppose $f$ and $g$ are functions from $\mathbb N^+$ to itself. I want to consider the function $f^g$, where $f^g(n) = f \circ \dots \circ f(n)$, where composition is done $g(n)$-many times. Note tha …
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
11
votes
1
answer
765
views
What can the extremely large cardinals tell us about small sets?
Are there any applications of the largest large cardinals to consistency results concerning, say, cardinals below $\aleph_{\aleph_\omega}$? Or perhaps to prove results in descriptive set theory? I a …
13
votes
5
answers
1k
views
A generalization of metric spaces
Let $(L,<,+)$ be a structure such that (1) $<$ is a linear order of $L$, (2) $L$ has a least element 0, (3) $+$ is a binary function on $L$ that behaves like addition of positive real numbers, i.e. co …
8
votes
Accepted
Demuth's theorem in set theory
I'm not sure if this specific claim is stated explicitly anywhere, but it follows from the more general discussion about intermediate extensions in Jech, page 247. If we take any $x \in L[r]$, then th …
8
votes
1
answer
436
views
Hahn’s theorem on ordered fields
There is a theorem attributed to Hahn that every ordered field $F$ containing $\mathbb R$ is a subfield of a formal power series field $\mathbb R[[X^\Gamma]]$, where $\Gamma$ is an ordered abelian gro …
7
votes
0
answers
182
views
rigidity of $\mathcal P(\omega_1) / NS$ under MA
In Woodin's book, Lemma 5.100 asserts that if $MA_{\omega_1}$ holds and there is an $\omega_2$-saturated ideal $I$ on $\omega_1$, then $\mathcal P(\omega_1)/I$ is a rigid boolean algebra, meaning it h …
5
votes
1
answer
246
views
Forcing square introduces diamond
Let $\mathbb S_\kappa$ be the standard forcing for $\square_\kappa$ by initial segments. This is $(\kappa+1)$-strategically closed.
Observation: Let $T \subseteq \kappa^+$ be stationary. If $T$ …
6
votes
Accepted
Have axioms / axiom schemata of this flavour been proposed or otherwise considered?
Axiom: $0^\sharp$ exists.
$0^\sharp$ is a pivotal principle in the large cardinal hierarchy, but it is actually a set of natural numbers. If it exists, it is unique.
2
votes
Suslin algebras
Jech, Thomas J.
Some combinatorial problems concerning uncountable cardinals.
Ann. Math. Logic 5 (1972/73), 165–198.
Section 5 contains the forcing for arbitrarily big Suslin algebras. See also:
…
1
vote
1
answer
136
views
Ergodic theorem on limit of periodic transformations?
Suppose $(X,\mu)$ is a probability space, and $T_n, n \in \mathbb N$, is a sequence of periodic measure preserving transformations. For $x \in X$ and $f : X \to \mathbb R$, let $\mathrm{avg}_{f,n}(x) …
3
votes
1
answer
263
views
tree property at $\aleph_2$ and $\aleph_4$
It is claimed that if there are two weakly compact cardinals, then there is a generic extension in which $\aleph_2$ and $\aleph_4$ have the tree property. Assuming one knows Mitchell's forcing, what …