Imprimitive flag-transitive symmetric designs

A recent paper of O'Reilly Regueiro obtained an explicit upper bound on the number of points of a flag-transitive, point-imprimitive, symmetric design in terms of the number of blocks containing two points. We improve that upper bound and give a complete list of feasible parameter sequences for such designs for which two points lie in at most ten blocks. Classifications are available for some of these parameter sequences.     

The classification of flag-transitive Steiner 4-designs

Among the properties of homogeneity of incidence structures flag-transitivity obviously is a particularly important and natural one. Consequently, in the last decades flag-transitive Steinert-designs (i.e. flag-transitive t-(v,k,1) designs) have been investigated, whereas only by the use of the classification of the finite simple groups has it been possible in recent years to essentially characterize all flag-transitive Steiner 2-designs. However, despite the finite simple group classification, for Steiner t-designs with parameters t > 2 such characterizations have remained challenging open problems for about 40 years (cf. [11, p. 147] and [12 p. 273], but presumably dating back to around 1965). The object of the present paper is to give a complete classification of all flag-transitive Steiner 4-designs. Our result relies on the classification of the finite doubly transitive permutation groups and is a continuation of the author's work [20, 21] on the classification of all flag-transitive Steiner 3-designs. 2000 Mathematics Subject Classification. Primary 51E10 . Secondary 05B05 . 20B25     

The Aleksandrov problem in linear 2-normed spaces

We introduce the concept of 2-isometry which is suitable to represent the notion of area preserving mappings in linear 2-normed spaces. And then we obtain some results for the Aleksandrov problem in linear 2-normed spaces.     

On the Mazur-Ulam problem in linear 2-normed spaces

We study the notion of 2-isometry which is suitable to represent the concept of area preserving mapping in linear 2-normed spaces, and then prove the Mazur-Ulam problem in linear 2-normed spaces.     

Biplanes with flag-transitive automorphism groups of almost simple type,with classical socle

In this paper we prove that if a biplane D admits a flag-transitive automorphism group G of almost simple type with classical socle, then D is either the unique (11,5,2) or the unique (7,4,2) biplane, and G≤PSL ₂(11) or PSL ₂(7), respectively. Here if X is the socle of G (that is, the product of all its minimal normal subgroups), then X⊴G≤Aut G and X is a simple classical group.     

A characterization of truncated projective geometries as flag-transitive PG *.PG-geometries

We prove that every flag-transitive locally finite (PG ^*.PG)-geometry is a truncated projective geometry. Dedicated to Daniel Hughes on the occasion of his 80th birthday.     

交错群与旗传递点本原非对称2-（v，k，3）设计

受旗传递2-(v,k,3)对称设计和非对称2-(v,k,2)设计有关分类结果的启发,本论文继续研究旗传递非对称2-(v,k,3)设计.文章利用置换群的理论和组合设计的数量性质,借助计算机代数软件Gap和Magma,完全分类了自同构群G旗传递点本原,且基柱Soc(G)为交错群An(n≥5)的非对称2-(v,k,3)设计,证明了此类设计只能是唯一的2-(5,3,3)设计,且G=A_5或S_5.     

New classes of permutation binomials and permutation trinomials over finite fields

Permutation polynomials over finite fields play important roles in finite fields theory. They also have wide applications in many areas of science and engineering such as coding theory, cryptography, combinatorial design, communication theory and so on. Permutation binomials and permutation trinomials attract people's interest due to their simple algebraic forms and additional extraordinary properties. In this paper, we find a new result about permutation binomials and construct several new classes of permutation trinomials. Some of them are generalizations of known ones.     

Biplanes with flag-transitive automorphism groups of almost simple type,with exceptional socle of Lie type

In this paper we prove that there is no biplane admitting a flag-transitive automorphism group of almost simple type, with exceptional socle of Lie type. A biplane is a (v,k,2)-symmetric design, and a flag is an incident point-block pair. A group G is almost simple with socle X if X is the product of all the minimal normal subgroups of G, and X⊴G≤Aut (G). Throughout this work we use the classification of finite simple groups, as well as results from P.B. Kleidman’s Ph.D. thesis which have not been published elsewhere.