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This tag is used if a reference is needed in a paper or textbook on a specific result.

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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.
Monroe Eskew's user avatar
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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?
Monroe Eskew's user avatar
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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_ …
Monroe Eskew's user avatar
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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 …
Monroe Eskew's user avatar
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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
Monroe Eskew's user avatar
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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 …
Monroe Eskew's user avatar
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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 …
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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 …
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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 …
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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 …
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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 $T$ …
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6 votes
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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.
Monroe Eskew's user avatar
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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: …
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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) …
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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 …
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