A topological group is a group endowed with a topology such that the group operation and inversion are continuous maps. They are useful in various areas of mathematics. Every topological vector space is a topological group. Locally compact groups are important in harmonic analysis.

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If a normal subgroup, N, contains a lattice why does G/N have finite measure?

Suppose $G$ is a locally compact Hausdorff topological group and suppose $H \leq N \leq G$ are closed subgroups with $N$ normal. Now suppose $G/H$ has a finite $G$-invariant Boreal measure (in the ...
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32 views

A question on the right translation

Here is a claim: Let $G$ be a right topological group and $g$ be any element of $G$. Then the right translation $R_g$ of $G$ by $g$ is a homeomorphism of the space $G$ onto itself. How can I ...
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47 views

Is true that $Z(G)/N = Z(G/N)$ for connected topological groups?

Let $G$ be a connected topological group and $N$ a discrete normal subgroup of $G$. Is it true that $Z(G)/N = Z(G/N)$, where $Z(G)$ denotes the center of $G$? I know that every discrete normal ...
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1answer
88 views

Haar measure, convolution and involutions

I have some problems to follow the proof of the anti commutativity property of the convolution and involution operations defined using a Haar measure as presented in Pedersen's book "analysis Now", ...
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1answer
55 views

Combining the axioms of a topological group

According to Wikipedia, a topological group $G$ is a topological space and a group, such that the functions $$(x,y) \mapsto x\cdot y\\x\mapsto x^{-1} $$are continuous. Is the single requirement that ...
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39 views

Characters of Topological Group of $\mathbb{R}^n$

I am seeking to show that if $\phi :\mathbb{R}^n\rightarrow\mathbb{C}$ is a character of the topological group $\mathbb{R}^n$ then $\phi$ must have the form $\phi(x)=e^{ix\cdot\xi}$ for some $\xi$ in ...
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1answer
25 views

Action of discrete subgroups E(n) on $\Bbb{R}^n$

Isometry group of euclidean space $\Bbb{R}^n$ is displayed by E(n). We say that a subgroup G of E(n) is discrete if and only if the subspace topology (from E(n)) on G is discrete. If X and Y are ...
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H = {A $\in$ G| there exists f:[0,1]$\to$G continuous, such that f(0)=A, f(1)=I}, Is H normal in G?

If G is a subgroup of GL(n;$\mathbb R$) and H = {A $\in$ G| there exists f:[0,1]$\to$G continuous, such that f(0)=A, f(1)=I}, Is H normal in G?
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150 views

What is an awesome book as an introduction to hyper groups

I'm a grad studen and i'm choosing an area to follow on my doctorate (in?) and I've been thinking about extension of topological group theory results to topological hypergroups, but for that i need to ...
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36 views

Is every regular paratopological group completely regular?

This problem is presented as an open problem 1.31. on p.26 of Arhangel'skii-Tkachenko, Topological groups and related structures. Is this problem still open?
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Analytic/Smooth/Continuous maps between a manifold and itself

Let us suppose that $M_{\omega}$ is a connected real-analytic manifold of dimension $n$. Then there is an associated smooth structure, $\mathcal{C}^r$ structure ($r$ non-negative integer) on it. Let ...
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186 views

What's so cool about local compactness?

As I study more algebraic number theory, I hear more and more often about local compactness: locally compact fields, locally compact topological groups, Stone-Čech compactification of locally compact ...
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1answer
137 views

Discrete subgroups of isometry group $\mathbb{R}^n$

Let $G$ be a Hausdorff topological group. We say that a subgroup $S$ of $G$ is discrete if and only if the subspace topology (from $G$) on $S$ is discrete. Note that isometry group of euclidean space ...
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97 views

Is a regular Borel measure on a locally compact space necessarily $\sigma$-finite?

I am trying to compile a proof of the uniqueness of Haar measure. Usually this is done by multiple-integral mumbo-jumbo, abusing left and right invariance of two potential measures and invoking ...
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1answer
24 views

Neighborhood in topological groups

Let $G$ be a topological group, $e$ the neutral element and $U$ a neighborhood of $e$. Claim: Then there exists a neighborhood $V$ of $e$, such that $V^2 \subseteq U$. This should follow easily from ...
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178 views

equation involving the integral of the modular function of a topological group

Let $G$ be a locally compact topological group and $H$ a closed subgroup. Choose a left Haar measure $d\zeta$ for $H$, and let $d\mu$ be any measure for $G$. Also let $f$ and $g$ be continuous ...
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65 views

Is there a local group that is not locally isomorphic to a topological group?

Let $\:\langle \hspace{.02 in}\mathbf{U},\hspace{-0.03 in}\mathcal{T}_u\rangle\:$ be a Hausdorff space. $\;\;\;$ Let $\hspace{.02 in}\Gamma\hspace{.02 in}$ be a closed subset of $\hspace{.04 ...
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68 views

extension of group operation from $\mathbb{Q}$ to $\mathbb{R}$

I'm having a hard time with this (seems easy, but could be misleading) problem: Let $A \subseteq \mathbb{Q}$ be a convex subset, and let $+$ group operation on $A$. Let $\overline{A} := \{x \in ...
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1answer
46 views

Familiarizing with the Grothendieck topos $\mathbf{B}G$.

I am trying to familiarize with the Grothendieck topos $\mathbf{B}G$ of continuous $G$-sets, where $G$ is a topological group. I am unfortunately not very familiar with working with different ...
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158 views

Is $G$ a lie group if left multiplication is smooth and multiplication is smooth near $e$?

Suppose $G$ is a smooth manifold and also a topological group. Also suppose that left multiplication $L_g : G \rightarrow G$ is smooth for any $g \in G$. Finally suppose that the multiplication map is ...
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38 views

Prove uniqueness of Haar measure without using the integral?

All the literature I have seen proves the Haar measure is unique by first defining the Haar integral and then using Fubini's Theorem etc. to show that any two Haar integrals are scalar multiples of ...
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51 views

Different profinite topologies on a group?

I have some general questions around the profinite topology on a group $G$. On the page http://groupprops.subwiki.org/wiki/Profinite_topology one can read, that The profinite topology on a group is ...
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56 views

Subgroup Separability translated in Profinite Topology

The normal definition of subgroup separability is: A group $G$ is said to be subgroup separable if for every finitely generated subgroup $H\leq G$ and $g\in G\setminus H$ there exists a subgroup of ...
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92 views

Why is $\mathbb R^n$ under the Zariski topology not a topological group?

Reasons that $(\mathbb R^n, +, \mathcal Z)$ is not a topological group: Given any two distinct points $\vec{p},\vec q \in \mathbb R ^n$ let $P$ be the unique hyperplane through $\vec p$ which is ...
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210 views

Product of totally disconnected space is totally disconnected?

I read that the cartesian product with the product topology of a family of totally disconnected topological spaces is totally disconnected, too. Is that true? How are the connected components in the ...
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2answers
74 views

Topological Group $G$ totally disconnected $\Rightarrow$ $G$ hausdorff?

On Wikipedia, I read that a topological group is necessarily Hausdorff if it is totally disconnected. Is that true? I read it on this page: http://en.wikipedia.org/wiki/Totally_disconnected_group ...
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42 views

Group operation continuous in the interval topology

I'm trying to prove the following: We have a DLO without endpoints M, and a group operation on M, which is continuous in the interval topology. I want to prove: if $b<c$ then for every $a \in M$ ...
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1answer
70 views

Is Steinhaus theorem ever used in topological groups?

Steinhaus theorem in $\mathbb{R}^d$ says that for $E\subset\mathbb{R}^d$ with positive measure, $E-E:=\{x-y:x,y\in E\}$ contains an open neighborhood of the origin. And for locally compact Hausdorff ...
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47 views

Is the following homomorphism continuous?

Let $G$ be a closed, torsion-free and divisible subgroup of locally compact abelian group $X$ such that $nX=G$ for some $n$. For $x\in X$, there exist $g\in G$ such that $nx=ng$. So we can define a ...
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86 views

topological group that is connected and locally connected but not path-connected

Is there a $\hspace{.01 in}\big($T$_{\hspace{.01 in}0}$$\hspace{-0.02 in}\big)\hspace{.01 in}$ topological group that is connected and locally connected but is not path-connected? (This question ...
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1answer
82 views

Are Compact Sets Separated In a Locally Compact Topological Group

I am studying a proof of the existence of Haar measure on locally compact groups. http://www.albanyconsort.com/HaarMeasure/HaarMeasure.pdf In this proof (at the top of page 7) when proving finite ...
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120 views

Discrete Closed Subgroup H of a Simply Connected Topological Group G isomorphic to fundamental group of G / H.

A problem in Rotman's Algebraic Topology is as follows: Given a simply connected topological group G with a closed discete normal subgroup H, show that $\pi_1(G / H) \cong H$. I believe I have this ...
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1answer
56 views

Uncountable dense measurable subgroups of $\mathbb{C}$

Is it possible to have an uncountable proper dense subgroup of $\mathbb{C}$ which is also Baire or Lebesgue measurable?
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43 views

right multiplication by elements of a discrete subgroup preserve left haar measure?

If $\Gamma$ is a discrete subgroup of a locally compact topological group, G, it is not necessarily the case that right multiplication on $G$ by elements of $\Gamma$ will preserve a left Haar ...
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94 views

Orientability as a topological property

Can one prove that orientability(of a manifold)is a topological property without using algebraic topology? That is, using a combination of general topology,linear algebra,and topological groups(such ...
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53 views

invariant measure on a quotient of a topological group

Suppose I have a locally compact topological group, $G$, and a closed subgroup $H\leq G$. Suppose $\Delta _G|_H = \Delta_H$ where the $\Delta$ are the modular functions on $G$ and $H$. How can I see ...
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1answer
109 views

Mal'cev completion of nilpotent groups

Is the $\mathbb{R}$-Mal'cev completion of a finitely generated torsion free nilpotent group connected and simply connected?. Thanks!
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115 views

Good book for studying $S_\infty$.

I'm looking for any books with some good information involving $S_\infty$ and other Polish groups. Specifically interested in $S_\infty$. This is an extremely amazing topological group, now having ...
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1answer
43 views

A topological group question about generators

If $G$ is connected topological group and $e \in V$, $V$ is open. Then prove that $V$ is a set of generators for $G$.
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1answer
64 views

Double Coset Closed

Let $G$ be a locally compact group and $H$ a closed subgroup. Under what conditions can we say that the double cosets $H\cdot x \cdot H$ are closed? Is this always true? I am interested mainly in the ...
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108 views

Connected subgroups of SU(2) and SU(3)

I am reading 'Lie groups, Lie Algebras, and Representations : An Introduction' by Brian Hall and am unable to do the problem 17 in chapter 3. It says Show that every connected Lie subgroup of ...
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102 views

Finding a certain subsemigroup of $(\mathbb R,+)$ [closed]

Is there a subsemigroup $A$ of $(\mathbb R,+)$ such that it has a limit point and has no intersect with its limit points? Thanks for any hints.
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1answer
47 views

Is the following descending sequence nonzero?

Let $K_{1}\supseteq K_{2}\supseteq K_{3}\supseteq \cdots$ be a descending sequence of compact subgroups of compact, torsion-free group $G$. Is $\bigcap_{r=1}^\infty n^r K\neq 0$? (for a positive ...
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34 views

Compact subset of compactly generated group

Let $G$ be a locally compact topological group, that is also Hausdorff and second countable. Let $S$ be a compact subset that generates $G$ as a group, which contains the identity and is closed under ...
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1answer
150 views

Proving that a metric space is a group

I'm stuck on this relatively hard problem. Let $G$ be a non-empty set, $d$ a distance on $G$ and $\cdot$ an associative operation on $G$ $\cdot$ is such that $$\forall a \in G , \forall x \in G ...
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1answer
49 views

Question about $S_\infty$ or $Aut(\mathbb{N})$

I have been reading a little Kechris and other random Polish group books, and have come across a question I just can't wrap my mind around. Show that $S_\infty$ or $Aut(\mathbb{N})$ the set of all ...
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1answer
175 views

$G$ topological group, $H$ discrete normal subgroup, $p$ projection, form Covering Space.

Let $G$ be a topological group. Let $H$ be a discrete normal subgroup of $G$. Let $p : G \to G/H$ be the projection map. Show that $(G, p, G/H)$ form a covering space. Here is what I have so far: ...
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1answer
52 views

Is $SL_1(D)$ toplogically finitely generated, for $D$ a division algebra over a local field?

I've been struggling with this one all day, and I was wondering if someone can give me a hand with the proof. I'm not even sure if the group in question is finitely generated, so I would appreciate if ...
2
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1answer
59 views

Finitely generated subgroups of prodiscrete groups

Suppose $(G_n, p_{n+1,n}:G_{n+1}\to G_n)$ is an inverse sequence of discrete groups and (obviously continuous) group homomorphisms. Let $G=\varprojlim G_n$ be the inverse limit (with the usual inverse ...
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1answer
54 views

Compactness in a short exact sequence of topological groups

Suppose $H,G,K$ are abelian Hausdorff topological groups and $0\to H\overset{\alpha}\to G\overset{\beta}\to K\to 0$ an exact sequence of continuous homomorphisms. If $H$ and $K$ are compact, can we ...