The groups related to the smallest non-affine Hall triple system

Every HTS is associated with a M₃-loop, just as every affine space overF ₃ is associated with an elementary abelian 3-group. If E is a M₃-loop, denote by(E) the corresponding HTS. Then ¦ Aut (E) ¦=¦E¦.¦Aut E ¦. When E is free among the M₃-loops which are nilpotent of class 2, the groups Aut E and Aut (E) may be described. The Fischer groups related to the non-affine HTS of order 3⁴ are described and the structure of their automorphism groups is discussed.     

Interstitial and pseudo gaps in models of Peano Arithmetic

In this paper we study the automorphism groups of models of Peano Arithmetic. Kossak, Kotlarski, and Schmerl [9] shows that the stabilizer of an unbounded element a of a countable recursively saturated model of Peano Arithmetic M is a maximal subgroup of Aut(M) if and only if the type of a is selective. We extend this result by showing that if M is a countable arithmetically saturated model of Peano Arithmetic, Ω ? M is a very good interstice, and a ∈ Ω, then the stabilizer of a is a maximal subgroup of Aut(M) if and only if the type of a is selective and rational (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Automorphisms of Countable Recursively Saturated Models of PA: Open Subgroups and Invariant Cuts

Let M be a countable recursively saturated model of PA and H an open subgroup of G = Aut(M). We prove that I(H) = sup {b ∈ M : (?? ∈ G\H) ?u < b fu = u and J(H) = inf{b ∈ M H} may be invariant, i. e. fixed by all automorphisms of M.     

The Similarity Between Finitary and Artinian-Finitary Groups

Let M be a module over the commutative ring R. The finitary automorphism group of M over R is FAut_RM = {g ? Aut_RM :M(g-1) is R-Noetherian}{\rm FAut}_RM =\{g\in{\rm Aut}_RM :M(g-1)\ {\rm is}\ R\hbox{-}{\rm Noetherian}\} and the Artinian-finitary automorphism group of M over R is F₁Aut_RM = {g ? Aut_RM : M(g-1) is R-Artinian}.{\rm F}_1{\rm Aut}_RM = \{g\in{\rm Aut}_RM : M(g-1)\ {\rm is}\ R\hbox{-}{\rm Artinian}\}. We investigate further the surprisingly close relationship between these two types of automorphism groups. Their group theoretic properties seem practically identical.     

The Similarity Between Finitary and Artinian-Finitary Groups

Let M be a module over the commutative ring R. The finitary automorphism group of M over R is and the Artinian-finitary automorphism group of M over R is We investigate further the surprisingly close relationship between these two types of automorphism groups. Their group theoretic properties seem practically identical.     

Automorphisms of commutative Moufang loops satisfying the minimality condition

We consider commutative Moufang loops Q with multiplicative group M satisfying the minimality condition for its subloops. Such loops, as well as the class of such loops, are characterized by various subgroups of automorphism groups Aut Q and Aut M. We study the structure of the groups Aut Q and Aut M and prove that these groups have matrix representations.     

Finitary groups and Krull dimension over the integers

Let M be any Abelian group. We make a detailed study for reasons explained in the Introduction of the normal subgroup

Aut(X, σ) and Aut(X/σ) are not isomorphic in the category of surfaces with nodes

A symmetric Riemann surface is a pair (X,?σ) where X is a Riemann surface and?σ?is an anticonformal involution. We denote by Aut(X,?σ) the subgroup of Aut(X) defined by the automorphisms commuting with σ. There is a natural isomorphism between Aut(X,?σ) and Aut(X/σ). In this article we shall show that this isomorphism does not stand if X is a Riemann surface with nodes.     

The finite simple groups with at most two fusion classes of every order

Elements a,b of a group G are said to be fused if a = b^σ and to be inverse-fused if a =(b^-1)^σ for some σ ? Aut(G). The fusion class of a ? G is the set {a^σ | σ ? Aut(G)}, and it is called a fusion class of order i if a has order iThis paper gives a complete classification of the finite nonabelian simple groups G for which either (i) or (ii) holds, where:

(i) G has at most two fusion classes of order i for every i (23 examples); and

(ii) any two elements of G of the same order are fused or inversenfused.

The examples in case (ii) are: A₅, A₆,L₂(7),L₂(8), L₃(4), Sz(8), M₁₁ and M₂₃An application is given concerning isomorphisms of Cay ley graphs.     

Complex<Emphasis Type="BoldItalic">n</Emphasis>-dimensional manifolds with a real<Emphasis Type="BoldItalic">n</Emphasis><Superscript>2</Superscript>-dimensional automorphism group

The main theorem of this article is a characterization of non compact simply connected complete Kobayashi hyperbolic complex manifold of dimension n≽ 2 with real n ²-dimensional holomorphic automorphism group. Together with the earlier work [11, 12] and [13] of Isaev and Krantz, this yields a complete classification of the simply-connected, complete Kobayashi hyperbolic manifolds with dim_ℝ Aut (M) ≽ (dim_ℂ M)².     

Behavior of Distant Maximal Geodesics in Finitely Connected Complete Two-Dimensional Riemannian Manifolds II

We study the behavior of maximal geodesics in a finitely connected complete two-dimensional Riemannian manifold M admitting curvature at infinity. In the case where M is homeomorphic to ² the Cohn–Vossen theorem states that the total curvature of M, say c(M), is 2. We already studied the case c(M)<2 in our previous paper. So we study the behavior of geodesics in M with total curvature 2 in this paper. Next we consider the case where M has nonempty boundary. In order to know the behavior of distant geodesics in M with boundary, it is useful to investigate the 'visual image' of the boundary of M. The latter half of this paper will be spent to study the asymptotic behavior of the visual image of a subset of M with located point tending to infinity.     

Automorphisms of Relatively Free Nilpotent Lie Algebras

Let L be a relatively free nilpotent Lie algebra over ? of rank n and class c, with n ≥ 2; freely generated by a set 𝒵. Give L the structure of a group, denoted by R, by means of the Baker–Campbell–Hausdorff formula. Let G be the subgroup of R generated by the set 𝒵 and N _Aut(L)(G) the normalizer in Aut(L) of the set G. We prove that the automorphism group of L is generated by GL _n (?) and N _Aut(L)(G). Let H be a subgroup of finite index in Aut(G) generated by the tame automorphisms and a finite subset X of IA-automorphisms with cardinal s. We construct a set Y consisting of s + 1 IA-automorphisms of L such that Aut(L) is generated by GL _n (?) and Y. We apply this particular method to construct generating sets for the automorphism groups of certain relatively free nilpotent Lie algebras.     

Krieger factors isomorphic to their tensor square and pure point spectrum flows

A factor M, isomorphic to its tensor square, whose Sakai flip σ? Aut(M ? M) is approximately inner, has a flow of weights with pure point spectrum.     

On automorphisms of A-groups

Let G be an A-group (i.e. a group in which xx ^α  = x ^α x for all and let denote the subgroup of Aut(G) consisting of all automorphisms that leave invariant the centralizer of each element of G. The quotient is an elementary abelian 2-group and natural analogies exist to suggest that it might always be trivial. It is shown that, in fact, for any odd prime p and any positive integer r, there exist infinitely many finite pA-groups G for which has rank r. Received: 23 March 2008, Revised: 20 May 2008     

Automorphisms of direct products of finite groups

This paper shows that if H and K are finite groups with no common direct factor and G = H × K, then the structure and order of Aut G can be simply expressed in terms of Aut H, Aut K and the central homomorphism groups Hom (H, Z(K)) and Hom (K, Z(H)). Received: 18 April 2005; revised: 9 June 2005     

Matroid automorphisms of the root system <Emphasis Type="Italic">H</Emphasis><Subscript>3</Subscript>

Let H ₃ be the root system associated with the icosahedron, and let M(H ₃) be the linear dependence matroid corresponding to this root system. We prove , and interpret these automorphisms geometrically. Dedicated to Thomas Brylawski.     

Rational representations of Yangians associated with skew Young diagrams

Consider the general linear group GL_M over the complex field. The irreducible rational representations of the group GL_M can be labeled by the pairs of partitions and such that the total number of non-zero parts of and does not exceed M. Let EQ4 be the irreducible representation corresponding to such a pair. Regard the direct product as a subgroup of GL_N+M . Take any irreducible rational representation of GL_N+M. The vector space comes with a natural action of the group GL_N. Put n=. For any pair of standard Young tableaux of skew shapes respectively, we give a realization of as a subspace in the tensor product of n copies of defining representation of GL_N, and of ñ copies of the contragredient representation ()^*. This subspace is determined as the image of a certain linear operator on W_nñn. We introduce this operator by an explicit multiplicative formula. When M=0 and is an irreducible representation of GL_N, we recover the known realization of as a certain subspace in the space of all traceless tensors in . Then the operator may be regarded as the rational analogue of the Young symmetrizer, corresponding to the tableau of shape . Even when M=0, our formula for is new. Our results are applications of the representation theory of the Yangian of the Lie algebra . In particular, is an intertwining operator between certain representations of the algebra on . We also introduce the notion of a rational representation of the Yangian . As a representation of , the image of is rational and irreducible.Mathematics Subject Classification (2000): 17B37, 20C30, 22E46, 81R50in final form: 10 July 2003     

On Stabilizers Of Some Moieties Of The Random Tournament

Any countably infinite tournament T₀ embeds as a moiety of the random tournament T in such a way that its setwise stabilizer in Aut(T) is isomorphic to Aut(T₀).     

Group Theoretic Properties of the Group of Computable Automorphisms of a Countable Dense Linear Order

We compare Aut(Q), the classical automorphism group of a countable dense linear order, with Aut _c (Q), the group of all computable automorphisms of such an order. They have a number of similarities, including the facts that every element of each group is a commutator and each group has exactly three nontrivial normal subgroups. However, the standard proofs of these facts in Aut(Q) do not work for Aut _c (Q). Also, Aut(Q) has three fundamental properties which fail in Aut _c (Q): it is divisible, every element is a commutator of itself with some other element, and two elements are conjugate if and only if they have isomorphic orbital structures.