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Questions about abstract measure and Lebesgue integral theory. Also concerns such properties as measurability of maps and sets.

15 votes
1 answer
2k views

Is "conditioning to a sub-$\sigma$-algebra" a measurable operation?

Let $\mathcal{B}$ be the Borel $\sigma$-algebra of $[0,1]$, and let $\mathcal{M}$ be the set of probability measures on $([0,1],\mathcal{B})$, equipped with the evaluation $\sigma$-algebra $\ \sigma(\ …
Julian Newman's user avatar
9 votes
0 answers
255 views

Is the inverse of a measurably parametrised family of bijections between standard Borel spac...

It is known that a measurable bijection $f \colon [0,1] \to [0,1]$ has a measurable inverse. (Here, all measurability is simply with respect to the Borel $\sigma$-algebra of $[0,1]$.) Now fix an arbi …
Julian Newman's user avatar
9 votes
1 answer
859 views

Do the Lebesgue-null sets cover "all the sets can naturally be regarded as sort-of-null sets"?

Let $F$ be the set of bijective Borel-measurable functions $f \colon [0,1] \to [0,1]$ that preserve the Lebesgue measure. Is it the case that for every non-Lebesgue-measurable set $A \subset …
Julian Newman's user avatar
8 votes
3 answers
819 views

Do regular conditional distributions almost surely assign trivial measure to all members of ...

Let $(X,\Sigma)$ be a standard measurable space, let $\rho$ be a probability measure on $(X,\Sigma)$, and let $\mathcal{E}$ be a sub-$\sigma$-algebra of $\Sigma$. We will say that a stochastic kernel …
Julian Newman's user avatar
8 votes
3 answers
690 views

Is "the purely probabilistic version of Freiling's axiom of symmetry" disprovable in ZFC?

I'm trying to pinpoint the "intuitive argument" for Freiling's Axiom of Symmetry. It's meant to be a "probabilistic" argument, so thinking about what seems to me to be the probabilistic intuition, it …
Julian Newman's user avatar
7 votes
1 answer
304 views

Can the integral of a "generic" bounded measurable function be determined by its values on t...

[This question is an extension of my question Does a positive-measure subset of the unit interval almost surely intersect a random translation of some countable subgroup of $\mathbb{R}$?. I'm asking i …
Julian Newman's user avatar
5 votes
1 answer
243 views

Is the topology of weak+Hausdorff convergence Polish?

Let $X$ be a compact metric space, $P_X$ the set of Borel probability measures on $X$, and $K_X$ the set of non-empty closed subsets of $X$. I will define the "topology of weak+Hausdorff convergence" …
Julian Newman's user avatar
4 votes
Accepted

Is "conditioning to a sub-$\sigma$-algebra" a measurable operation?

Okay, I think I've worked out that the answer is no, i.e. there exists a sub-$\sigma$-algebra $\mathcal{G}$ of $\mathcal{B}$ such that $\mathbb{E}_\mathcal{G}$ is not universally measurable. (We will …
Julian Newman's user avatar
4 votes
0 answers
218 views

Does it make sense to regard the graph of any function as being a "sort-of-null set"?

Following the nice answer to Do the Lebesgue-null sets cover "all the sets can naturally be regarded as sort-of-null sets"?, the particular situation that I am especially interested in (which is a kin …
Julian Newman's user avatar
4 votes
Accepted

Do regular conditional distributions almost surely assign trivial measure to all members of ...

I've found the answer - it's NO! The paper I found addressing the question is the following: http://projecteuclid.org/euclid.aop/1175287757 ("0-1 Laws for Regular Conditional Probabilities") A simple …
Julian Newman's user avatar
3 votes
1 answer
314 views

Can a weaker version of the Hausdorff paradox be proved without AC?

The Hausdorff paradox is an incredibly counter-intuitive consequence of the axiom of choice; it is also important for demonstrating the non-existence, under AC, of a rotation-invariant measure on the …
Julian Newman's user avatar
3 votes
Accepted

Convergence of Radon Nikodym derivatives

I'm going to assume that your space is locally compact (as well as $\sigma$-compact), so that $X$ is the union of a sequence of compact sets where each lies in the interior of the next. In this case, …
Julian Newman's user avatar
3 votes
1 answer
446 views

"Strongly mutually singular" families of measures, and the set of ergodic measures

Let $(X,\Sigma)$ be a measurable space [which we can assume to be a standard Borel space if we wish]. Let $\mathcal{S}$ be a set of probability measures on $(X,\Sigma)$. [If we wish, we can assume th …
Julian Newman's user avatar
2 votes
1 answer
610 views

Does a positive-measure subset of the unit interval almost surely intersect a random transla...

Please forgive me if this is a very easy question. Let $A \subset [0,1]$ be a Borel-measurable set with strictly positive Lebesgue measure. Does there necessarily exist a countable subgroup $G$ of $\ …
Julian Newman's user avatar
2 votes
0 answers
244 views

Reference for Borel $\sigma$-algebra of topology of convergence in probability

I'm pretty sure I can prove the "Theorem" given further below (without very much difficulty), but it seems way too basic not to have been noticed before. So I'm wondering if there are any papers/text …
Julian Newman's user avatar

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