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Everything the deals with properties and definitions of Haar measure, as well as related fields when the question relies heavily on the notion of haar measure - group harmonic analysis, group ergodic theory etc.

16 votes
Accepted

Are Hausdorff measures on the real line Haar measures for some locally compact topology?

The answer is NO because the Euclidean and the discrete topologies are the unique locally compact group topologies on $\mathbb R$, which are stronger that the Euclidean topology of the real line. Th …
Taras Banakh's user avatar
  • 41.8k
5 votes
0 answers
213 views

On generically Haar-null sets in the real line

First some definitions. For a Polish space $X$ by $P(X)$ we denote the space of all $\sigma$-additive Borel probability measures on $X$. The space $P(X)$ carries a Polish topology generated by the s …
Taras Banakh's user avatar
  • 41.8k
4 votes
Accepted

Is the sumset of two Haar positive closed subsets of a Polish group non-meager?

I have just realized that this my question has a simple negative answer: Denote by $\mathbb R_+=[0,\infty)$ the half-line. Observe that the countable product of lines $G=\mathbb R^\omega$ is an Abelia …
Taras Banakh's user avatar
  • 41.8k
3 votes
Accepted

Haar-null union of dense subsets

In the Frechet space $X:=\mathbb R^\omega$ consider the dense linear subspace $$L_0:=\{(x_n)_{n\in\omega}\in\mathbb R^\omega:|\{n\in\omega:x_n\ne0\}|<\omega\}.$$ Fix a countable base $\{V_n\}_{n\in\o …
Taras Banakh's user avatar
  • 41.8k
3 votes
1 answer
197 views

Is the sumset of two Haar positive closed subsets of a Polish group non-meager?

A famous Steinhaus theorem says that if measurable subsets $A,B$ of a locally compact topological group $G$ have positive Haar measure, then the difference $AA^{-1}$ is a neighborhood of the unit and …
Taras Banakh's user avatar
  • 41.8k
2 votes
0 answers
102 views

Is this concrete set generically Haar-null?

This question is related to this problem on MO about generically Haar-null sets in locally compact Polish groups but is more concrete. First we recall the definition of a generically Haar-null set in …
Taras Banakh's user avatar
  • 41.8k
1 vote

Haar measurable sets and quotient maps

It seems that the answer to this problem is affirmative for compact groups. Indeed, if the union $E$ of $H$-cosets is measurable in $G$, then for every $\epsilon>0$ we can find two compact subsets $A\ …
Taras Banakh's user avatar
  • 41.8k