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10:47 AM
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A: Axiom of Choice: Ultrafilter vs. Vitali set

luckycan you tell me how to construct a nonmeasurable set from a free (non-principal) ultrafilter on ω?

There are several posts related to this topic:
7
Q: Relationships between AC, Ultrafilter Lemma/BPIT, Non-measurable sets

Forever MozartHow is it possible to reconcile the following... In 1970, Solovay constructed Solovay's model, which shows that it is consistent with standard set theory, excluding uncountable choice, that all subsets of the reals are measurable. A not too well known application of the Boolean prime ide...

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Q: Non-measurability of ultrafilter on $\omega$

BurakIt is well-known that any non-principal ultrafilter on $\omega$ is non-measurable regarded as a subset of $2^{\omega}$. My question is "how well-known" is this fact? Here is the only proof I know: Let $\mathcal{U}$ be a non-principal ultrafilter on $\omega$. If $\mathcal{U}$ were measurable, the...

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Q: Does the existence of a non-principal measure on ω imply that of a non Lebesgue measurable set?

Jean-Claude SikoravA non-principal [probability] measure on a set X is a function $\mu$ defined on all subsets of $X$, with values in $[0,1]$, which is finitely additive, satisfies $\mu(X)=1$, and vanishes on singletons. Can one prove in ZF + DC that the existence of such a measure on $\bf N$ (or on $\omega$), th...

@lucky Your posts is probably going to be deleted, since it is not really an answer. However, you can find some pointers to your question here in chat. (You do not have sufficient reputation to talk in chat, but any user can read the chat transcript.) — Martin Sleziak 1 min ago
 
11:02 AM
You can find an argument in this answer: mathoverflow.net/a/57108/1946. — Joel David Hamkins 1 min ago
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A: A remark of Connes

Joel David Hamkins ...as soon as you have a non-standard number, you get a non-measurable set. Every nonstandard natural number $N$ gives rise to a nonprincipal ultrafilter $U$ on $\mathbb{N}$, by saying that a set $X\subset\mathbb{N}$ is in $U$ if and only if $N\in X^*$, the nonstandard analogue of $X$. In ot...

This is perhaps also somewhat related - since an ultrafilter can be viewed as a finitely-additive measure:
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Q: Ref. request: Additive probability measure on $\mathcal P({\bf N})$ supplies subset of $\mathbf R$ without Baire property

Salvo TringaliZFC proves, among the other things, the existence of a (finitely) additive probability measure $\theta: \mathcal P(\mathbf N) \to \mathbf R$ on the power set of $\mathbf N$ such that $\theta(X) = 0$ for every finite $X \subseteq \mathbf N$, which I will shortly refer to as an ADPM (where "D" stan...

 

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