On the length of a finite group and of its 2-generator subgroups

The nonsoluble length λ(G) of a finite group G is defined as the minimum number of nonsoluble factors in a normal series of G each of whose quotients either is soluble or is a direct product of nonabelian simple groups. The generalized Fitting height of a finite group G is the least number h = h* (G) such that F* _h (G) = G, where F* ₁ (G) = F* (G) is the generalized Fitting subgroup, and F* _i+1(G) is the inverse image of F* (G/F*_i (G)). In the present paper we prove that if λ(J) ≤ k for every 2-generator subgroup J of G, then λ(G) ≤ k. It is conjectured that if h* (J) ≤ k for every 2-generator subgroup J, then h* (G) ≤ k. We prove that if h* (〈x, x^g 〉) ≤ k for allx, g ∈ G such that 〈x, x^g 〉 is soluble, then h* (G) is k-bounded.     

On automorphism groups of Cayley graphs

LetX _G,H denote the Cayley graph of a finite groupG with respect to a subsetH. It is well-known that its automorphism groupA(X_G,H) must contain the regular subgroupL _G corresponding to the set of left multiplications by elements ofG. This paper is concerned with minimizing the index [A(X_G,H)L_G] for givenG, in particular when this index is always greater than 1. IfG is abelian but not one of seven exceptional groups, then a Cayley graph ofG exists for which this index is at most 2. Nearly complete results for the generalized dicyclic groups are also obtained.     

Existence Theorem for the Discontinuous Generalized Quasivariational Inequality Problem

We consider the following generalized quasivariational inequality problem: given a real Banach space E with topological dual E* and given two multifunctions G:X2 ^X and F:X2 ^E *, find such that

Generalized bisymmetry on a restricted domain

Let X ⊂ ℝ be an interval of positive length and define the set Δ = {(x, y) ∈ X × X | x ≧ y}. We give the solution of the equation

On the Discontinuous Infinite-Dimensional Generalized Quasivariational Inequality Problem

In this paper, we deal with the following generalized quasivariational inequality problem: given a real normed space E with topological dual E* and two multifunctions G: X→2 ^X and F: X→2 ^E*, find $\left( {\hat x,\hat \phi } \right)$ ∈X × E* such that $\hat x \in G\left( {\hat x} \right),{\text{ }}\hat \phi \in F\left( {\hat x} \right),{\text{ }}\left\langle {\hat \phi ,\hat x - y} \right\rangle \leqslant 0,{\text{for all }}y \in G\left( {\hat x} \right).$ We extend to such infinite-dimensional setting some existence results which have been obtained recently for the special case where E is finite dimensional. In particular, our assumptions do not imply any kind of continuity for the multifunction F.     

Finite extensions of free pro-P groups of rank at most two

For a pro-p groupG, containing a free pro-p open normal subgroup of rank at most 2, a characterization as the fundamental group of a connected graph of cyclic groups of order at mostp, and an explicit list of all such groups with trivial center are given. It is shown that any automorphism of a free pro-p group of rank 2 of coprime finite order is induced by an automorphism of the Frattini factor groupF/F ^* . Finally, a complete list of automorphisms of finite order, up to conjugacy in Aut(F), is given. Supported by an NSERC grant. Supported by the Austrian Science Foundation.     

Convolution tails,product tails and domains of attraction

Summary A distribution function is said to have an exponential tail F(t) = F(t, ) if e ^u F(t+u) is asymptotically equivalent to F(t), t, t, for all u. In this case F(lnt) is regularly varying. For two such distributions, F and G, the convolution H=F*G also has an exponential tail. We investigate the relationship between H and its components F and G, providing conditions for lim H/F to exist. In addition, we are able to describe the asymptotic nature of H when the limit is infinite, for many cases. This corresponds to determining both the domain of attraction and the norming constants for the product of independent variables whose distributions have regularly varying tails.In addition, we compare the tails of H=F*G with H ₁=F ₁*G ₁when F is asymptotically equivalent to F and G is equivalent to G ₁. Such a comparison corresponds to the balancing consideration for the product of independent variables in stable domains of attraction. We discover that there are several distinct comparisons possible.     

Sparse <Emphasis Type="Italic">H</Emphasis>-Colourable Graphs of Bounded Maximum Degree

Let F be a graph of order at most k. We prove that for any integer g there is a graph G of girth at least g and of maximum degree at most 5k¹³ such that G admits a surjective homomorphism c to F, and moreover, for any F-pointed graph H with at most k vertices, and for any homomorphism h from G to H there is a unique homomorphism f from F to H such that h=fc. As a consequence, we prove that if H is a projective graph of order k, then for any finite family of prescribed mappings from a set X to V(H) (with ||=t), there is a graph G of arbitrary large girth and of maximum degree at most 5k^26mt (where m=|X|) such that and up to an automorphism of H, there are exactly t homomorphisms from G to H, each of which is an extension of an f.Supported in part by the National Science Council under grant NSC89-2115-M-110-012Final version received: June 9, 2003     

On the homotopy fixed point problem for free loop spaces and other function complexes

Let G be a finite group, let X and Y be finite G-complexes, and suppose that for each K G, Y ^K is dim(X ^K)-connected and simple. G acts on the function complex F(X, Y) by conjugation of maps. We give a complete analysis of the homotopy fixed point set of the space F(X, Y). As a corollary, we are able to analyze at a prime p, the homotopy fixed point set of the circle action on X, where X denotes the free loop space of X, and X is a simply connected finite complex.Supported in part by NSF DMS 86-02430.To A. Grothendieck on the occasion of his sixtieth birthday     

The Picard group of a complex quotient variety

For a holomorphic action of a reductive complex Lie groupG on a Stein complex spaceX the map onto the categorical quotientX//G induces a mapPic(X//G)Pic(X) between the groups of holomorphic line bundles. Sufficient conditions are given for the injectivity of this map. The results are gained from a consideration of the relations between the cohomology rings (with values in ) ofX andX//G via Leray spectral sequence.     

The primitive ideal space of solvable Lie groups

LetG be a connected and simply connected solvable Lie group. In a previous paper (cf.[22]) we associated withG a familyM of geometrical objects (generalized orbits), and with each elementO ofM a unitary equivalence classF(O) of factor representations. IfG is nilpotent,M coincides with the orbit space of the coadjoint representation, and the mapOF(O) reproduces essentially the Kirillov isomorphism betweenM and the dual ofG. As a fargoing extension of this, the principal result of the present paper asserts, that upon assigning to 0M the kernel of the representation, associated with some element ofF(O), of the groupC ^* algebraC ^*(G), we obtain a bijection betweenM and the primitive ideal space ofC ^*(G).This work was supported by a grant from the National Science Foundation     

Existence of finitely dominatedCW-complexes withG 1(X) = π1(X) and non-vanishing finiteness obstruction

We show for a finite abelian groupG and any element in the image of the Swan homomorphism sw: that it can be realized as the finiteness obstruction of a finitely dominated connectedCW-complexX with fundamental group π₁(X) =G such that π₁(X) is equal to the subgroupG ₁(X) defined by Gottlieb. This is motivated by the observation that anyH-spaceX satisfies π₁(X) =G ₁(X) and still the problem is open whether any finitely dominatedH-space is up to homotopy finite.     

On perfectt-shift codes in abelian groups

LetG be a finite abelian group,t a positive integer. Thet-shift sphere with centerx G is the setS _t (x)={±ix|i=1,...,t}. At-shift code is a subsetX ofG such that the setsS _t (x) (x X) have size 2t and are disjoint. Clearly, the sphere packing bound: 2t|X|+1|G| holds for anyt-shift codeX. Aperfect t-shift code is at-shift codeX with 2t|X|+1=|G|. A necessary and sufficient condition for the existence of a perfectt-shift code in a finite abelian group is known fort-1, 2. In this paper, we determine finite abelian groups in which there exists a perfectt-shift code fort=3, 4.This research was completed during the author's visit at the Institute for System Analysis, Moscow, as a Heizaemon Honda fellow of the Japan Association for Mathematical Sciences.     

Generalized elements of best approximation

It is proved that generalized elements of best approximation (GEBA's) are approximated by minimizing nets in the(X^**, X^*) topology. Criteria for GEBA's are established. GEBA's are considered in ^* where is a 1-normalizing subspace of X^*.Translated from Matematicheskie Zametki, Vol. 19, No. 4, pp. 513–523, April, 1976.     

On thin-complete ideals of subsets of groups

Let F ì P_G \mathcal{F} \subset {\mathcal{P}_G} be a left-invariant lower family of subsets of a group G. A subset A ⊂ G is called F \mathcal{F} -thin if xA ?yA ? F xA \cap yA \in \mathcal{F} for any distinct elements x, y ∈ G. The family of all F \mathcal{F} -thin subsets of G is denoted by t( F ) \tau \left( \mathcal{F} \right) . If t( F ) = F \tau \left( \mathcal{F} \right) = \mathcal{F} , then F \mathcal{F} is called thin-complete. The thin-completion t^*( F ) {\tau^*}\left( \mathcal{F} \right) of F \mathcal{F} is the smallest thin-complete subfamily of P_G {\mathcal{P}_G} that contains F \mathcal{F} . Answering questions of Lutsenko and Protasov, we prove that a set A ⊂ G belongs to τ*(G) if and only if, for any sequence (g _n ) _n∈ω of nonzero elements of G, there is n ∈ ω such that

Generalization of a criterion for semistable vector bundles

It is known that a vector bundle E on a smooth projective curve Y defined over an algebraically closed field is semistable if and only if there is a vector bundle F on Y such that both H⁰(X,EF) and H¹(X,EF) vanishes. We extend this criterion for semistability to vector bundles on curves defined over perfect fields. Let X be a geometrically irreducible smooth projective curve defined over a perfect field k, and let E be a vector bundle on X. We prove that E is semistable if and only if there is a vector bundle F on X such that Hⁱ(X,EF)=0 for all i. We also give an explicit bound for the rank of F.     

Uniqueness of norm on L(G) and C(G) when G is a compact group

Let G be a compact group. If the trivial representation of G is not weakly contained in the left regular representation of G on L₀²(G) and X is either L^p(G) for 1<p?∞ or C(G), then we show that every complete norm |·| on X that makes translations from (X,|·|) into itself continuous is equivalent to ||·||_p or ||·||_∞ respectively. If 1<p?∞ and every left invariant linear functional on L^p(G) is a constant multiple of the Haar integral, then we show that every complete norm |·| on L^p(G) that makes translations from (L^p(G),|·|) into itself continuous and that makes the map t?L_t from G into bounded is equivalent to ||·||_p.     

Dimensions of irreducible modules over twisted group algebras

LetN be a normal subgroup of a finite groupG, letF be an algebraically closed field, letZ ²(G, F ^*) and letV be an irreducible module over the twisted group algebraF . If charF=p>0 divides (GN), assume thatG/N isp-solvable. It is proved that dim _F V divides (GN)d whered is the dimension of an irreducible constituent ofV _N. The special case where=1 andN is abelian yields a well-known theorem of Dade [3]. Another special case, namely whereN is abelian, charF(GN) and the restriction of ofNxN is a coboundary is a generalization of the main result of Ng [5].     

Modification of a Finsler space by a normalized semi-parallel vector field

LetF _n be a Finsler space with metric functionF(x, y). M. Matsumoto [6] has defined a modified Finsler spaceF _n ^* whose metric functionF ^*(x, y) is given byF ^*2 = = F² + (X_i(x)yⁱ)², whereX _i are the components of a covariant vector which is a function of coordintae only. Since a concurrent vector is a function of coordinate only, Matsumoto and Eguchi [9] have studied various properties of the modified Finsler spaceF _n ^* under the assumption thatX _i are the components of a concurrent vector field inF _n. In this paper we shall introduce the concept of semi-parallel vector field inF _n and study the properties of modified Finsler spaceF _n ^* .