Enumerating Transitive Finite Permutation Groups

Denote by f(n) the number of subgroups of the symmetric groupSym(n) of degree n, and by f_trans(n) the number of its transitivesubgroups. It was conjectured by Pyber [9] that almost all subgroupsof Sym(n) are not transitive, that is, f_trans(n)/f(n) tendsto 0 when n tends to infinity. It is still an open questionwhether or not this conjecture is true. The difficulty comesfrom the fact that, from many points of view, transitivity isnot a really strong restriction on permutation groups, and thereare too many transitive groups [9, Sections 3 and 4]. In thispaper we solve the problem in the particular case of permutationgroups of prime power degree, proving the following result.1991 Mathematics Subject Classification 20B05, 20D60.     

Fixed-Point-Free p-Elements in Transitive Permutation Groups

We give sufficient conditions for a finite permutation groupto contain a fixed-point-free permutation of p-power order fora given prime p.     

Asymptotic Results for Transitive Permutation Groups

In this paper we give answers to some open questions concerninggeneration and enumeration of finite transitive permutationgroups. In [1], Bryant, Kovács and Robinson proved thatthere is a number c^' such that each soluble transitive permutationgroup of degree n2 can be generated by elements, and later A. Lucchini [5] extended thisresult (with a different constant c') to finite permutationgroups containing a soluble transitive subgroup. We are nowable to prove this theorem in full generality, and this solvesthe question of bounding the number of generators of a finitetransitive permutation group in terms of its degree. The resultobtained is the following. 1991 Mathematics Subject Classification20B05, 20D60.     

On the Movement of Transitive Permutation p-Groups

Let G be a transitive permutation group on a set and m a positive integer. If | – | m for every subset of and all g G, then || 2mp/(p – 1) where p is the least odd prime dividing |G|. It was shown by Mann and Praeger [13] that, for p = 3, the 3-groups G which attain this bound have exponent p. In this paper we will show a generalization of this result for any odd primes.AMS Subject Classification (2000), 20BXX     

On Transitive Permutation Groups with Primitive Subconstituents

Let G be a transitive permutation group on a set such that,for , the stabiliser G induces on each of its orbits in \{}a primitive permutation group (possibly of degree 1). Let Nbe the normal closure of G in G. Then (Theorem 1) either N factorisesas N=GG for some , , or all unfaithful G-orbits, if any exist,are infinite. This result generalises a theorem of I. M. Isaacswhich deals with the case where there is a finite upper boundon the lengths of the G-orbits. Several further results areproved about the structure of G as a permutation group, focussingin particular on the nature of certain G-invariant partitionsof . 1991 Mathematics Subject Classification 20B07, 20B05.     

传递系统中的不变攀援集

推广了攀援集的概念.研究了传递系统中的不变攀援集.证明了在相当广泛的条件下,一个传递系统有一个不变的稠密的σ-Cantor子集是完全攀援集.     

Transitive Permutation Groups with Cyclic Point Stabilizers of Maximum Order

We prove that a transitive permutation group of degree n with a cyclic point stabilizer and whose order is n(n-1) is isomorphic to the affine group of degree 1 over a field with n elements. More generally we show that if a finite group G has an abelian and core-free Hall subgroup Q, then either Q has a small order (2|Q|² < |G|) or G is a direct product of 2-transitive Frobenius groups.     

Solvable Permutation Groups and Orbits on Power Sets

We consider the class ? of finitely generated toral relatively hyperbolic groups. We show that groups from ? are commutative transitive and generalize a theorem proved by Benjamin Baumslag in [3 Baumslag, B. (1967). Residually free groups. Prceedings of the London Mathematical Society 17(3):402–418.[Crossref] , [Google Scholar]] to this class. We also discuss two definitions of (fully) residually-𝒞 groups, i.e., the classical Definition 1.1 and a modified Definition 1.4. Building upon results obtained by Ol'shanskii [18 Ol'shanskii, A. Yu. (1993). On residualing homomorphisms and G-subgroups of hyperbolic groups. International Journal of Algebra Computation 3:365–409.[Crossref] , [Google Scholar]] and Osin [22 Osin, D. V. (2010). Small cancellations over relatively hyperbolic groups and embedding theorems. Annals of mathematics 172:1–39.[Crossref], [Web of Science ®] , [Google Scholar]], we prove the equivalence of the two definitions for 𝒞 = ?. This is a generalization of the similar result obtained by Ol'shanskii for 𝒞 being the class of torsion-free hyperbolic groups. Let Γ ∈ ? be non-abelian and non-elementary. Kharlampovich and Miasnikov proved in [14 Kharlampovich, O., Myasnikov, A. (2012). Limits of relatively hyperbolic groups and Lyndon's completions. Journal of the European Math. Soc. 14:659–680.[Crossref], [Web of Science ®] , [Google Scholar]] that a finitely generated fully residually-Γ group G embeds into an iterated extension of centralizers of Γ. We deduce from their theorem that every finitely generated fully residually-Γ group embeds into a group from ?. On the other hand, we give an example of a finitely generated torsion-free fully residually-? group that does not embed into a group from ?; ? is the class of hyperbolic groups.     

一类数列积的解法及推广

对一类数列积进行求解并推广,使结果适用于一般数列积的计算.     

有限Chevalley群作用下的子代数轨道生成的格

讨论了一般情形Chevalley群作用下的子代数轨道生成的格.在同类型格中,研究了不同格之间的包含关系,并对格中子代数的特性及格的几何性进行了刻画.     

直觉模糊集的扩展原理

基于文[1]给出的直觉模糊集的截集、分解定理和表现定理,利用模糊集的扩展原理,本文建立了直觉模糊集的扩展原理.首先,给出了直觉模糊集的扩展原理及其等价形式;其次,讨论了直党模糊集的扩展原理的有关性质;最后,研究了复合函数的直觉模糊集扩展原理及其性质.     

Extension Operations on Sets of Leaf-Labeled Trees

A fundamental problem in classification is how to combine collections of trees having overlapping sets of leaves. The requirement that such a collection of trees is realized by at least one parent tree determines uniquely some additional subtrees not in the original collection. We analyze the "rules" that arise in this way by defining a closure operator for sets of trees. In particular we show that there exist rules of arbitrarily high order which cannot be reduced to repeated application of lower-order rules.     

直觉模糊集的扩张运算

在 K.Atanassov引进直觉模糊集概念的基础上 ,首先给出乘积的定义和扩张原理 ,并讨论群上的直觉模糊集的并、交等扩张运算 ;其次在两个经典群同态、同构的条件下 ,研究直觉模糊集乘积的扩张运算问题。     

模糊集乘积的扩张运算

在Zadeh的模糊集概念基础上,给出模糊集乘积同态映射的概念;其次,讨论模糊集乘积的性质;然后根据扩张原理,在模糊集乘积同态、同构映射的条件下,研究模糊集乘积与模糊集乘积同态像之间的关系.     

一类物元可拓集的性质研究

提出了物元等价类概念,并利用子集合X和属性子集R对物元集合S(U,A,V,f)在集合论域U上构造了一类可拓集合A~,并讨论了A~关于X和R的一些相关性质.