Elementarily free groups are subgroup separable
Henry Wilton
初等自由群是与自由群具有相同初等理论的有限生成群。我们证明了初等自由群是子群可分的，回答了Zlil Sela的一个问题。
Elementarily free groups are the finitely generated groups with the same elementary theory as free groups. We prove that elementarily free groups are subgroup separable, answering a question of Zlil Sela.
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Subgroups of direct products of elementarily free groups
我们利用Zlil Sela的描述结构的群体具有相同的基本理论的自由群：他们和他们的numerous产生的子群形成一个规定的子类E的双曲极限群。证明了若$G_1,...,G_n$在E中，则子群$Γ\subset G_1\times...\times G_n$是$\FP_n$型的当且仅当$Γ$是它自身，直到有限指数，至多是来自$\mathcal E$的$n$群的直积.这回答了塞拉的一个问题。
We study to what extent torsion-free (Gromov)-hyperbolic groups are elementarily equivalent to their finite index subgroups. In particular, we prove that a hyperbolic limit group either is a free product of cyclic groups and surface groups, or admits infinitely many subgroups of finite index which are pairwise non elementarily equivalent.
Reid asked whether all convex-cocompact subgroups of mapping class groups are separable. Using a construction of Manning-Mj-Sageev, we give examples of separable convex-cocompact subgroups that are free of arbitrary finite rank, while prior examples seem to all be virtually cyclic.
Separable subgroups of mapping class groups
本文研究了曲面的映射类群的几类著名子群的可分性。
Elementary equivalence of endomorphism rings and automorphism groups of periodic Abelian groups
该研究探讨周期阿贝尔群的自同态环与自同构群的初等等价问题，给出了自同态环初等等价的充要条件，并针对特定周期阿贝尔群刻画了自同构群初等等价的等价条件。
In this paper, we give a complete characterization on which finitely generated subgroups of finitely generated $3$-manifold groups are separable. Our characterization generalizes Liu's spirality character on $π_1$-injective immersed surface subgroups of closed $3$-manifold groups. A consequence of our characterization is that, for any compact, orientable, irreducible and $\partial$-irreducible $3$-manifold $M$ with nontrivial torus decomposition, $π_1(M)$ is LERF if and only if for any two adjacent pieces in the torus decomposition of $M$, at least one of them has a boundary component with gen…
A group $G$ is called subgroup conjugacy separable if for every pair of non-conjugate finitely generated subgroups of $G$, there exists a finite quotient of $G$ where the images of these subgroups are not conjugate. It is proved that the fundamental group of a hyperbolic 3-manifold (closed or with cusps) is subgroup conjugacy separable.
Separation of Relatively Quasiconvex Subgroups
假设所有双曲群都是剩余有限的。以下声明如下：在相对双曲群中，拟凸子群是可分的，其外围结构由非均匀生成的幂零子群组成;在秩1对称空间中，非均匀格的几何有限子群是可分的; Kleinian群是子群可分的。我们还证明了有限体积双曲3-流形的LERF将遵循闭双曲3-流形的LERF。方法是通过组合定理和填充定理将相对双曲群G的拟凸子群的可分性约化为双曲商G/N的拟凸子群的可分性。然后应用Agol、Groves和Manning的结果。
Let $π$ be a set of primes. We show that $π$-separable groups have a conjugacy class of subgroups which specialize to Carter subgroups, i.e. self-normalizing nilpotent subgroups, or equivalently, nilpotent projectors, when specializing to soluble groups.
A group $G$ is called subgroup conjugacy separable if for every pair of non-conjugate finitely generated subgroups of $G$, there exists a finite quotient of $G$ where the images of these subgroups are not conjugate. We prove that limit groups are subgroup conjugacy separable. We also prove this property for one relator groups of the form $R=\langle a_1,...,a_n\mid W^n\rangle$ with $n>|W|$. The property is also proved for virtual retracts (equivalently for quasiconvex subgroups) of hyperbolic virtually special groups.
On subgroup separability of free-by-cyclic and deficiency 1 groups
本文证明了多项式增长单演的自由循环群在特定条件下子群可分，并指出随机亏度1群大概率不可分。
Separable subgroups have bounded packing
本文证明了可分子群在环境群中有界填充。有界包装的概念是由Hruska和Wise提出的，特别是，我们的结果肯定地回答了他们的一个问题，即问一个虚多环群的每个子群是否具有有界包装性质。
We explore the extent to which constructing the inductive theory of $\mathfrak{X}$-submaximal subgroups is possible. To this end, we study the behavior of $π$-submaximal subgroups under homomorphisms with $π$-separable kernels and construct examples where such behavior is irregular.
On D. I. Moldavanskii's question about $p$-separable subgroups of a free group
证明了非交换的自由群都有一个在幂零群类中不可分的非交换生成孤立子群。这使我们能够对D. I. Moldavanskii在“Kourovka笔记本”：这是真的，任何生成的$p'$ -孤立子群的自由群是可分的类有限$p$ -群？
We prove that if a countable group is elementarily equivalent to a non-abelian free group and all of its abelian subgroups are cyclic, then the group is a union of a chain of regular NTQ groups (i.e., hyperbolic towers).
We prove that cyclic subgroup separability is preserved under exponential completion for groups that belong to a class that includes all coherent RAAGs and toral relatively hyperbolic groups; we do so by exploiting the structure of these completions as iterated free products with commuting subgroups. From this we deduce that the cyclic subgroups of limit groups over coherent RAAGs are separable, answering a question of Casals-Ruiz, Duncan and Kazachov. We also discuss relations between free products with commuting subgroups and the word problem, and recover the fact that limit groups over cohe…
Suppose that a group $G$ acts non-elementarily on a hyperbolic space $S$ and does not fix any point of $\partial S$. A subgroup $H\le G$ is said to be geometrically dense in $G$ if the limit sets of $H$ and $G$ coincide and $H$ does not fix any point of $\partial S$. We prove that every invariant random subgroup of $G$ is either geometrically dense or contained in the elliptic radical (i.e., the maximal normal elliptic subgroup of $G$). In particular, every ergodic measure preserving action of an acylindrically hyperbolic group on a Borel probability space $(X,μ)$ either has finite stabilizers…
Nonstandard free groups
本文通过非标准解释方法，研究了非标准自由群及群的非标准模型，揭示了超幂结构与自然数非标准模型的关系，并引入非标准组合群论的基本概念。
Isotypical equivalence of periodic Abelian groups
本文研究了周期阿贝尔群的同型等价问题，提出了刻画该等价关系的不变量，并证明了具有可分约化部分的阿贝尔$p$-群同型等价的充要条件及其强齐次性。
Commensurability and separability of quasiconvex subgroups
我们表明，两个均匀的格子的一个规则的直角Fuchsian建筑是可折叠的，提供的室是一个多边形，至少有六个边缘。我们证明了在任意Gromovv-双曲正则直角建筑中，如果一个均匀格的拟凸子群是可分的，那么它与一个有限群的图积是可分的.对于Gromov-双曲二维Coxeter群的Davis复形的一致格，我们得到了类似的结果。我们还证明了CAT（0）平方复形的一致格被有限群的每个扩张实际上是平凡的，只要格的每个拟凸子群是可分的。
Let N be a finitely generated normal subgroup of a Gromov hyperbolic group G. We establish criteria for N to have solvable conjugacy problem and be conjugacy separable in terms of the corresponding properties of G/N. We show that the hyperbolic group from F. Haglund's and D. Wise's version of Rips's construction is hereditarily conjugacy separable. We then use this construction to produce first examples of finitely generated and finitely presented conjugacy separable groups that contain non-(conjugacy separable) subgroups of finite index.
Product separability in central extensions
本文研究了中心扩张在子群可分离性和双余集可分离性下的性质，证明了在特定条件下中心扩张的乘积可分离性和双余集可分离性的等价性及稳定性。
Locally Compact Groups with All Dense Subgroups Separable
该研究探讨所有稠密子群均可分的局部紧群的可度量化问题，构造反例说明局部紧阿贝尔群情形答案为负，证明连通紧群、代数阿贝尔紧群及子群全可分的局部紧群情形答案为正，并给出幂零群可度量化的必要条件。
Separable Subsets of GFERF Negatively Curved Groups
一个字双曲群$G$称为GFERF，如果每个拟凸子群与包含它的有限指数子群的交重合.我们证明了在任何这样的群中，n个拟凸子群的乘积在$G$上的profinite拓扑中是封闭的.
Separability in Morse local-to-global groups
本文证明在Morse局部到整体群中，稳定子群的可分性可传递到其乘积，并由此推出虚拟特殊群中稳定子群乘积的可分性。
Coxeter Groups, 2-Completion, Perimeter Reduction and Subgroup Separability
我们证明了在一个非常大的类Coxeter群的所有群体是局部拟凸的，并有一致的成员资格问题在二次时间可解。如果一个群满足进一步的假设，它是子群可分的，相关的同态也可以在二次时间内计算。该算法还决定了一个随机生成的子群是否具有有限指数。
A topological space is called {\it dense-separable} if each dense subset of its is separable. Therefore, each dense-separable space is separable. We establish some basic properties of dense-separable topological groups. We prove that each separable space with a countable tightness is dense-separable, and give a dense-separable topological group which is not hereditarily separable. We also prove that, for a Hausdorff locally compact group , it is locally dense-separable iff it is metrizable. Moreover, we study dense-subgroup-separable topological groups. We prove that, for each compact torsion …
On $p$-separability of subgroups of free metabelian groups
证明了每个自由亚交换非循环群都有一个在幂零群类中不可分的生成孤立子群。作为推论，我们证明了对每个素数$p$，任意自由亚阿贝尔非循环群都有一个非生成的$p'$-孤立子群，它不是$p$-可分的.
Elementary embeddings in torsion-free hyperbolic groups
本文研究了无挠无挠的双曲群中的嵌入，这类嵌入在一阶逻辑意义下是初等的。我们给出了一个描述这些嵌入在塞拉的双曲塔。作为推论，我们推出初等嵌入于群生成的自由群中的子群是自由因子.
On $\mathfrak{X}$-transitive groups and conjugate separable $\mathfrak{X}$-subgroups
本文研究了$\mathfrak{X}$-传递群和共轭分离的$\mathfrak{X}$-子群的结构及其与等式域和余$A$-自由群的关系，并证明了有限$\CSX$-群属于$\X$。
A profinite group is called small if it has only finitely many open subgroups of index n for each positive integer n. We show that every Frattini cover of a small profinite group is small. A profinite group is called strongly complete if every subgroup of finite index is open. We show that two profinite groups that are elementarily equivalent, in the first-order language of groups, are isomorphic if one of them is strongly complete, extending a result of Moshe Jarden and Alexander Lubotzky which treats the case of finitely generated profinite groups.
We find a condition on the underlying graph of an Artin group that fully determines if it is subgroup separable. As a consequence, an Artin group is subgroup separable if and only if it can be obtained from Artin groups of ranks at most 2 via a finite sequence of free products and direct products with the infinite cyclic group. This result generalizes the Metaftsis-Raptis criterion for Right-Angled Artin groups.
The cyclic subgroup separability of certain generalized free products of two groups
研究了两个剩余有限群的合并收缩的自由积。证明了这样一个群的循环子群是不可分的当且仅当它与一个在这个因子中不可分的自由因子的子群共轭。对于有限p-群类中的可分性，也得到了类似的结果。
Limit groups, positive-genus towers and measure equivalence
根据定义，一个$ω$ -剩余自由塔是正亏格的，如果在它的构造中使用的所有曲面都是正亏格的。证明了每个极限群实质上是正亏格$ω$ -无剩余塔的子群。将其与Gaboriau的结果相结合，证明了初等自由群与自由群是测度等价的.
In a remarkable series of papers, Zlil Sela classified the first-order theories of free groups and torsion-free hyperbolic groups using geometric structures he called towers. It was later proved by Chloé Perin that if $H$ is an elementarily embedded subgroup (or elementary submodel) of a torsion-free hyperbolic group $G$, then $G$ is a tower over $H$. We prove a generalization of Perin's result to toral relatively hyperbolic groups using JSJ and shortening techniques.
The residual closure of a subgroup $H$ of a group $G$ is the intersection of all virtually normal subgroups of $G$ containing $H$. We show that if $G$ is generated by finitely many cosets of $H$ and if $H$ is commensurated, then the residual closure of $H$ in $G$ is virtually normal. This implies that separable commensurated subgroups of finitely generated groups are virtually normal. A stream of applications to separable subgroups, polycyclic groups, residually finite groups, groups acting on trees, lattices in products of trees and just-infinite groups then flows from this main result.
On the cyclic subgroup separability of the free product of two groups with commuting subgroups
设G是群A和B与交换子群H \leqslant A和K \leqslant B的自由积，C是所有有限群的类或所有有限p-群的类.给出了G的所有C-可分循环子群的刻划，只要这个群是剩余的C-群。特别地，我们证明了：如果A，B是n-生成的幂零群，H，K在自由因子上是p '-孤立的，则G的所有p'-孤立循环子群在所有有限p-群类中是可分的.如果A、B是自由的，H、K是p ′-孤立的和循环的，同样的陈述也成立。
The Figure Eight Knot Group is Conjugacy Separable
证明了PGL（2，C）（抽象）可与欧氏Bianchi群同构的无无挠的子群是共轭可分的.因此，我们推导出标题中所述的结果。
Hall's Theorem for limit groups
马歇尔霍尔的一个著名定理。这意味着，所有的自由生成的自由群都是子群可分的，并且它们的所有的自由生成的子群都是有限指数子群的收缩。我们使用拓扑技术的启发工作Stallings证明，所有的极限群共享这两个属性。这回答了塞拉的一个问题。
We associate cube complexes called completions to each subgroup of a right-angled Coxeter group (RACG). A completion characterizes many properties of the subgroup such as whether it is quasiconvex, normal, finite-index or torsion-free. We use completions to show that reflection subgroups are quasiconvex, as are one-ended Coxeter subgroups of a 2-dimensional RACG. We provide an algorithm that determines whether a given one-ended, 2-dimensional RACG is isomorphic to some finite-index subgroup of another given RACG. In addition, we answer several algorithmic questions regarding quasiconvex subgro…
A well known theorem of Burns and Romanovskii states that a free product of subgroup separable groups is itself subgroup separable. We provide a proof using the language of immersions and coverings of graphs of groups, due to Bass.
Subgroup separability in integral group rings
给出了一个包含所有有限群$G$的有限群列表，使得整群环$\Z G$的单位群$\Z G^*$是子群可分的.只有两种类型的这些群$G$，我们不能决定是否$ZG^*$是子群可分的，即中心积$Q_8 Y D_8$和$Q_8\times C_p{with} p \text{prime and} p\equiv -1 \mod (8)$。
On the finitely separability of subgroups of generalized free products
证明了两个群的广义自由积的所有n-生成子群都是n-可分的，只要自由因子具有这一性质，且合并子群在相应的因子中正规，且满足子群的极大条件.
Subgroup separability in residually free groups
本文证明了剩余自由群的可表示子群是可分的，且$\mathrm{FP}_\infty$型子群是虚收缩的.本文描述了剩余自由群的可表示子群的成员问题的一个统一解。
One-relator groups with torsion are conjugacy separable
证明了具有挠率的单关系子群是遗传共轭可分的。我们的论点是基于Dani Wise和第一作者的最新结果的结合。作为推论，我们得到了具有挠率的单关系群的任何拟凸子群也是共轭可分的。
Order separability of HNN-extensions and free products with commutative subgroups
本文研究了HNN扩张和具有交换子群的自由积的序可分性。特别证明了具有极大连通循环子群的自由群的HNN扩张是2阶可分的。
Subgroups of monothetic groups
证明了每一个可分交换拓扑群与一个一元论群（即具有单个拓扑生成元的拓扑群）的拓扑子群同构。特别地，每个可分的可度量化的阿贝尔群嵌入到一个可度量化的一素群中。更一般地说，我们描述了所有可以嵌入到一元论群中的拓扑群：它们完全是阿贝尔拓扑群，其权$\leq\frak c$被每个非空开子集的可数个平移所覆盖。
Hereditary conjugacy separability of right angled Artin groups and its applications
证明了直角Artin群的有限指数子群是共轭可分的.然后，我们应用这个结果来建立其他类别的群的各种性质。特别地，我们证明了任何字双曲Coxeter群包含一个共轭可分子群的有限指数，并有一个剩余有限的外自同构群。主要结果的另一个推论是Bestvina-Brady群是共轭可分的，并且存在可解的共轭问题。
On the cyclic subgroup separability of free products of two groups with amalgamated subgroup
设$G$是两个群的自由积，其子群为合并子群，$π$是所有素数的集合或某个素数$p$的单元素集合\{ $p$ \}.用$Σ$表示群$G$的所有循环子群的族，这些循环子群在所有有限$π$ -群的类中是可分的。显然，自由因子的循环子群，不能在这些因子中被群$G$的有限$π$ -指数的所有正规子群族分离，与它们共轭的子群和所有不是$π^{\prime}$ -孤立的子群，不属于$Σ$。得到了$Σ$与群$G$的所有其它$π^{\prime}$ -孤立循环子群族重合的充分条件.特别地，证明了当自由因子是自由的或自由生成的剩余$p$ -有限幂零群时，循环合并自由积的剩余$p$ -有限性蕴涵了所有$p^{\prime}$ -孤立循环子群的$p$ -可分性.
Subgroup conjugacy separability for surface groups
一个群$G$称为子群共轭可分群（SCS），如果$G$的任意两个非共轭子群在$G$的某个有限商中保持非共轭.证明了可定向闭紧曲面的自由群和基本群是SCS。
A $σ$-McKay theorem for $π$-separable groups
本研究针对$π$-可分群证明了G. Navarro提出的McKay猜想的Hall $σ$-子群类比结论，该结论同时推广了经典McKay猜想及其$π$-可分版本，验证了相关不可约特征标计数等式。
Separability of Solvable Subgroups in Linear Groups
设G是特征为0的域上的非线性生成的线性群.设G的每一个可解子群都是循环的。然后，声称任何可解子群G是可分的。这一点在G=SL_n（Z）中得到了证明。然而，第4节中的主要定理的证明是不完整的。
Separability of unipotent-free abelian subgroups in linear groups
本文证明了在零特征域上的有限生成线性群中，无幂单阿贝尔子群具有可分性。
In this paper we further develop the theory of canonical approximations of Polishable subgroups of Polish groups, building on previous work of Solecki and Farah--Solecki. In particular, we obtain a characterization of such canonical approximations in terms of their Borel complexity class. As an application we provide a complete list of all the possible Borel complexity classes of Polishable subgroups of Polish groups or, equivalently, of the ranges of continuous group homomorphisms between Polish groups. We also provide a complete list of all the possible Borel complexity classes of the ranges…
On Subgroup Separability and Membership Problems in Twisted Right-Angled Artin Groups
本文仅通过定义混合图刻画了扭曲右角Artin群的子群可分性，推广了经典结果，并证明了凝聚群的子群成员判定问题可判定，同时解决了特定锥图族对应的有理与子半群成员判定问题。
On subgroup conjugacy separability in the class of virtually free groups
称群G为子群共轭可分群，如果G的任意两个非共轭生成的非共轭子群在G的某个有限商中保持非共轭。证明了有限群的有限树的自由群和基本群在某种正规化子条件下是SCS。引入子群的入共轭可分性，证明了上述群也具有这一性质。
Each second countable abelian group is a subgroup of a second countable divisible group
证明了定义在阿贝尔群$G$的子群$H$上的每个群都可以扩张为$G$上的群，使得所得到的伪可度量化拓扑群的密度一致.由此我们得到，任何$H$上的Hausdorff $ω$有界群拓扑都可以推广到$G$上的Hausdorff $ω$有界群拓扑.反过来，这个结果意味着每个可分可度量化阿贝尔群$H$是可分可度量化可除群$G$的子群。这个结果本质上依赖于选择公理，在决定性公理下是不正确的（它与选择公理矛盾，但隐含着可数的选择公理）。
In the present paper, the structure of a finite group $G$ having a nonnormal T.I. subgroup $H$ which is also a Hall $π$-subgroup is studied. As a generalization of a result due to Gow, we prove that $H$ is a Frobenius complement whenever $G$ is $π$-separable. This is achieved by obtaining the fact that Hall T.I. subgroups are conjugate in a finite group. We also prove two theorems about normal complements one of which generalizes a classical result of Frobenius.
Subgroup Conjugacy Separability in Residually Free Groups
本文研究剩余自由群的子群共轭性质，证明有限展示情形具有子群共轭可分性，$FP_\infty$ 型还具可辨识性，并推出其外自同构群剩余有限。
In this paper we study conjugacy separability of subdirect products of two free (or hyperbolic) groups. We establish necessary and sufficient criteria and apply them to fibre products to produce a finitely presented group $G_1$ in which all finite index subgroups are conjugacy separable, but which has an index $2$ overgroup that is not conjugacy separable. Conversely, we construct a finitely presented group $G_2$ which has a non-conjugacy separable subgroup of index $2$ such that every finite index normal overgroup of $G_2$ is conjugacy separable. The normality of the overgroup is essential in…
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