Questions tagged [gr.group-theory]
Questions about the branch of algebra that deals with groups.
8,182 questions
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A question on the poset of classes of isomorphic subgroups of finite groups
Given a finite group $G$, we consider the set $${\rm Iso}(G)=\{[H]\mid H\leq G\},$$where
$[H]=\{K\leq G\mid K\cong H\}, \forall H\leq G$. Then ${\rm Iso}(G)$ can be partially ordered by defining
$$[...
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Triangle groups [closed]
I am having a hard time finding references (apart from wikipedia) for the geometric interpretation of triangle groups $T_{a,b,c} = \langle x,y \mid |x|=a, |y|=b, |xy|=c \rangle$. How can these groups ...
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On generating Euler Square of index q, q-1 (where q is any prime power)
Can somebody help me in generating Euler Square of index q, q-1 (where q is any prime power). Also, kidly tell me if there is any code availeble for generating the stated Euler Square. The details of ...
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Existence of homogeneous single chain compositions of a given maximal subfactor?
All the subfactors here are irreducible inclusion of hyperfinite II$_1$ factors.
A subfactor $(N \subset M)$ is Homogeneous Single Chain ($HSC$) if its lattice of intermediate subfactors is a single ...
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Does $[H_i , G_i]$ distributive imply $[H_1 \times H_2, G_1 \times G_2]$ modular?
Let $L(G)$ be the subgroup lattice of $G$ and $[H, G]$ an interval in $L(G)$.
A lattice $(L, \wedge, \vee)$ is distributive if $a∨(b∧c) = (a∨b) ∧ (a∨c)$, $\forall a,b,c \in L $, and is modular if ...
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A formula for isotropy group $\pi_1(G_a)$
Let $G$ be a compact Lie group and $T$ be its maximal tours, and $a\in \mathfrak{g}^*$. and $G_a$ be the isotropy group of $G$ then $T\subset G_a$ and we know that $\pi_1(T)=\mathbb{Z}^n$. My ...
user21574
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A connection between nonplanar complete graphs and the alternating groups?
I didn't get any response on MSE so I though I'd give this a try here (my question on MSE).
I went to an undergrad's senior honors thesis presentation a while ago. She was discussing crossing numbers ...
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Finding stable ideals of $\mathbb{F}_3[[X,S]]$ by group action
Let $k > 1$ be a positive integer and define the action $\sigma_k$ on $\mathbb{F}_3[[X,S]]$ by:
$\sigma_k: X \mapsto X + S + X^k$
$\sigma_k: S \mapsto S + S^3$.
Conjecture: There exists a ...
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Can assigment of Cayley graphs be functorial?
Let $G$ and $G'$ be finitely generated groups and $f:G\to G'$ a homomorphism. First question: for a given $f:G\to G'$ it possible to select generating sets $S\in G, S'\in G'$ so that their would be a ...
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Do you know any clear classification of groups in which there would exist a unique non-linear character of a given degree?
According to
Lev Kazarin, On Thompson’s Theorem, Journal of Algebra 220, 574–590 (1999)
we know that:
[Corollary 5.3]:Let $$cd(G)=\{\chi(1)|\chi\in Irr(G)\}=\{1,f_1,\dots,f_n,d\}, \;\;n\gt0,$$
...
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irreducibility of exterior powers
Suppose I have a subgroup $H$ of $GL(V)$ such that $H$ acts irreducibly on all the exterior powers of $V$. Is there any sort of characterization of such things? (I am intentionally not specifying the ...
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on the open bruhat cell
Let $G$ a connected reductive group and $S=U^{-}TU$ the open cell.
Do we have $G=\bigcup\limits_{g\in G}gSg^{-1}$?
And also if I assume that $G$ is adjoint and $\overline{G}$ is the de Concini-...
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Is the automorphism group of a homogeneous (locally finite) tree unimodular?
I have seen somewhere (that I don't remember now) that the (full) automorphism group of a k-regular tree is unimodular. I assume a k-regular tree is the same thing as the homogeneous tree of degree k (...
user23860
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Amenability of the pair $(GL(2,\mathbb{Q})^+,SL(2,\mathbb{Z}))$
I am trying to see whether the pair $(GL(2,\mathbb{Q})^+,SL(2,\mathbb{Z}))$ is amenable in the following sense:
Let $H$ be a closed subgroup of a locally compact group $G$. The pair $(G,H)$ is called ...
user23860
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Are there algorithms and/or criteria for determining if a group has a presentation with all commutator relators?
Suppose $G = F/R$ is a finitely presented group with $F = F_n$ a free group and $R$ the normal closure of words $W_1, \dots, W_p$, not all of which are products of commutators. An obvious necessary ...
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The number of $p$-groups of order $\leq p^n$ that split over a normal abelian subgroup
How can one estimate the number of $p$-groups of order $\leq p^n$ that split over a normal abelian subgroup?
Moreover, let $s(n,p)$ be the number of such groups, and let $f(n,p)$ denotes the number ...
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Generator size for cyclic groups
Let $p$ be prime. Consider $\Bbb Z_{p}$, the cyclic multiplicative group.
Is it possible to choose a generator $c$ as small as $O(\log(p))$? (wiki shows $c$ as small as $O(\log^{6}(p))$ is possible ...
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Rank of normal closure of a subset
How does one find the rank of a normal closure of a subset?
In particular, I am studying this group: Let $K_n$ be the group with $n$ generators $x_1,\cdots,x_n$ satisfying the relation that each $x_i$...
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p-groups with isomorphic automophism groups.
Given a finite group $H$, How can one prove that the equation $Aut(X)=H$ has only finitely many solutions in the class of finite p-groups. (This would be the case if the divisibility conjecture is ...
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Nonlinear Operators(with the group property?)
Let V be a finitely generated vector space with dimension(V) = $n \in \mathbb{N}>1$. Now let T: $ V \to V$ be a map such that $\forall \hat{v},\hat{w} \in V$, $\; T(\hat{v}+\hat{w}) \neq T(\hat{v})+...
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automorphism group and group presentation
When does a group presentation of a group $G = < x_{1} , \ldots , x_{n} | r_{i}(x_{1} , \ldots , x_{n} ), \; 1 \leq i \leq k> $ produce all the elements of $Aut(G)$ by permuting the $x_{i}$?
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How many subgroups of order $\prod_{1}^{n} p_{i}^{n_{i}}$ are there in the finite product of cyclic groups?
All of the following ${p_{i},q_{i}}$are prime numbers, ${n,m,k}$ are pre-assigned integers.
Consider the product of cyclic groups $\prod_{1}^{n} \mathbb Z_{p_{i}^{n_{i}}}$ then we asked the question:
...
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Normal subgroups In a p-group [Reference?]
Dear Experts,
I'm a graduate student, dealing with group-theory.
In my current research, I used the bound "Alexander Gruber" wrote about in this post:
See Here
(Actually, I have just found out ...
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When are graphs of cohomologically complete groups cohomologically complete?
A group $G$ is cohomologically $p$- complete if the canonical map from $G$ to it's pro$-p$ completion $\hat G^p$ induces an isomorphism on cohomology $H^\ast_{cont}(\hat G^p, \mathbb{Z}_p) \rightarrow ...
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An almost permutation G-lattice
I've been trying to determine the rationality of certain fields of invariants coming from G-lattices. More precisely, letting $G$ be a finite group, $L=\mathbb{Z}^n$ a free abelian group with a $G$ ...
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Dimension of faithful irreducible representations of $\mathbb{Z}_q\rtimes \mathbb{Z}_{p^2}$ in characteristic p,q
Let $p,q$ be primes s.t. $q=np+1$. Denote $m=p^2$. Then $\mathbb{Z}_p$ acts non-trivially on $\mathbb{Z}_q$, so we have a non-abelian semi-direct product $\mathbb{Z}_q\rtimes \mathbb{Z}_m$, with the ...
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For which triples of cycle structures $\alpha,\beta,\gamma$ are there permutations $x,y$ with $C(x),C(y),C(xy)=\alpha,\beta,\gamma?$
This question is motivated by the answer to this one There is also another followup. The question there was " Given integers $m,n,k \gt 1$ construct permutations $x,y$ with $o(x)=m,o(y)=n$ and $o(x,y)=...
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does s.e.s 0->A->B->C->0 of profinite groups imply C=B/A and A<B topologically?
Assume $A, B, C$ are profinite groups and $0\to A\to B\to C\to 0$ is an exact sequence of continuous maps. Which of the following assertions follows?:
(i) the subspace-topology induced on $A$ via $A\...
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on a decomposition lemma in adelic groups
Let X a curve over an algebraically closed k.
Fix $x$ and $y$ two distinct closed points of X.
Let G be a connected reductive group over k.
We denote Spec $\hat{\mathcal{O}}_{X,x}$ the formal ...
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Outer automorphisms of an infinite simple group
Let $r(m)$ denote the residue class $r+m\mathbb{Z}$, where $0 \leq r < m$.
Given disjoint residue classes $r_1(m_1)$ and $r_2(m_2)$, let the class transposition
$\tau_{r_1(m_1),r_2(m_2)}$ be the ...
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A generalization of a group isomorphism.
Let $H,K$ be two normal subgoups of a group $G$.
We know that there exists a group isomorphism:
$HK\diagup H\simeq H\diagup{H\cap K}$.
I want to generalize this statement in the language of category ...
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Intersection of cocompact closed normal subgroups
Let $G$ be a locally compact Hausdorff topological group.
Definition A closed normal subgroup $H \unlhd G$ is called cocompact if $G/H$ is compact with respect to the quotient topology.
Note that ...
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What are natural automorphisms of set of subsets ? How to "constructify" Andreas Blass theorem on sets M,N with G action such that C[M] = C[N] as G modules ?
Consider vector space V over finite field $F_q$ and
$V^ * $ its dual space. Denote $P(V), P(V^ * )$ the sets of ALL subsets in $V$ and $V^*$.
Question How to construct GL_n(F_q) equivariant ...
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Subgroups of direct sum of a Prufer group
Hello,
I wonder which p-primary groups can be injected into a suitable direct sum of Prufer groups. I would suspect that ugly groups like the torsion part of $\prod \mathbb{Z}_{p^k}$ are not of this ...
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About union of conjugate proper subgroups in a math paper
My question is about the shaded area in this image.
Does the symbol $L=\bigcup_{g \in G} T^{g}$ means that $L$ is a union of sets or $L=\langle T^{g}, g\in G \rangle$? If it means the first one, then ...
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Number of Generators of [G,G] when G is free? [closed]
If $G$ is a free group on $n>1$ generators, then $[G,G]$ is also free, being a subgroup of a free group. Is there a formula for the number of generators of this free group in terms of n?
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Isomorphisms of group extensions arising from antisymmetric forms
Let $V,W$ be topological vector spaces and fix continuous antisymmetric bilinear forms $\omega_1:V\times V\to \mathbb{R}$, $\omega_2:W\times W\to\mathbb{R}$. Since $\omega_1$ is a 2-cocycle (in fact ...
- 1,411
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Derived Series & Frattini Series of a p-group/pro-p group
Does someone know of any work done regarding the connection between the derived series & the frattini series of a pro-p group/p -group ?
[ I'm aware of the general fact that the frattini-series ...
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Generalizing groups via the Hall-Witt identity
In studying the integrability problem for Lie algebra representations, I have been led to wonder whether generalizing the notion of group by dropping associativity, while keeping the Hall-Witt ...
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Totally singular subspaces in orthogonal vector spaces
This is for all that are interested in classical groups and their representations.
We are investigating the following situation:
Let $V$ be $d$-dimensional $k$-vector space (where $k$ is a finite ...
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Reference request: a verification of a nonstandard subgroup being a Tits subgroup.
I have a particular infinite-index subgroup $H$ of the genus 2 symplectic group $Sp(2, \mathbb{R})$. This subgroup is self-normalizing (ie. $gHg^{-1}=H$ only if $g\in H$). I am looking to determine ...
- 2,274
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Twisted homology of free products
Let $G_1$ and $G_2$ be groups and let $M$ be a vector space equipped with actions of $G_1$ and $G_2$. The free product $G_1 \ast G_2$ thus acts on $M$. How can one compute the twisted group homology ...
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Characterizing symplectic matrices relative to a partial Iwasawa decomposition
Fixing notation: for matrices $A,X$ we let $A[X]$ denote ${}^tXAX$.
Let $P_n$ denote the collection of real $n\times n$ positive definite symmetric matrices.
For $Y\in P_n$ we have the usual ...
- 2,274
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Determine the next number in the sequence
This problem originates from a programming interview problem. In that problem, we are asked to convert the array $[a_0, a_1, \cdots, a_{N-1}, b_0, b_1, \cdots, b_{N-1}, c_0, c_1, \cdots, c_{N-1}]$ ...
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Discrete subgroups of isometry group of proper metric space
Let $X$ be a proper metric space and consider its isometry group $\mathrm{ISO}(X)$ endowed with the compact-open topology. Let $G$ be a subgroup of $\mathrm{ISO}(X)$.
Consider the following ...
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Can we make a useful ring on an Elliptic curve? [closed]
I know that given an elliptic curve $E$ we can define an addition $+$ over the set of points on the curve to make in an abelian group. However
Can we define multiplication on $E$ in a natural way so ...
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Automorphisms of locally finite countable posets-2
Given is a locally finite countable connected poset which satisfies further the following properties:
Let $C$ be any maximal chain ( i.e. inextendible chain) and $A$ be any antichain. Then $A$ is ...
user16974
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Size of an abelian permutation group with generators of order 2 [closed]
Let $g_1, \ldots, g_k$ be distinct permutations on a set $\Omega$. Suppose that $G = \langle g_1, \ldots, g_k \rangle$ is an abelian permutation group with only elements of order at most 2. Is it ...
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Popular level article on monster group
People who are not mathematicians (or high school students who are in maths) often become interested in what is the Monster Group - mainly because of unusual name. Since it's not my field, I'm able ...