Ree群2G2(q)与2-(v,k,1)区组设计(Ⅱ)

本文证明了自同构群的基柱为Ree群2G2(q)的区-本原2-(v,k,1)设计必为Ree unital,即2-(q3+1,q+1,1)设计,从而部分地回答了Praeger问题.     

Ree群~2G_2(q)与2-(v,k,l)区组设计(Ⅱ)

本文证明了自同构群的基柱为Ree群~2G_2(q)的区-本原2-(v,k,1)设计必为Ree unital,即2-(q~3+1,q+1,1)设计,从而部分地回答了Praeger问题.     

Ree群~2G_2(q)与2-(v,k,l)区组设计(Ⅱ)

本文证明了自同构群的基柱为Ree群~2G_2(q)的区-本原2-(v,k,1)设计必为Ree unital,即2-(q~3+1,q+1,1)设计,从而部分地回答了Praeger问题.     

李型单群~2F_4(q~2)与2-(ν,κ,1)区组设计

本文证明了当2-(v,k,1)设计的自同构群G的基柱soc(G)=2F4(q2)时,Buekenhaut-Delandtsheer-Doyen猜想成立,即自同构群G的基柱为Ree群2F4(q2)的区本原2-(v,k,1)设计必为点本原的.     

李型单群2F4(q2)与2-((u),k,1)区组设计

本文证明了当2-((u),κ,1)设计的自同构群G的基柱soc(G)=2F4(q2)时,Buekenhaut-Delandtsheer-Doyen猜想成立,即自同构群G的基柱为Ree群2F4(q2)的区本原2-((u),k,1)设计必为点本原的.     

典型群PSU（3，q2）与2—（v,k,1）设计

讨论自同构群是酉群PSU（3,q2)(q=2^l)的区－本原的2-(v,k,1)设计,首先证明了它必是点－本原的,然后确定了这种类型的设计,即它只能为2－（q3 1,q 1,1)设计。     

区传递的2-(ν,κ,1)设计与李型单群E8(q)

分类自同构群的基柱为李型单群E8(q)的区传递2-(ν,κ,1)设计,得到如下定理:设D为一个2-(ν,κ,1)设计,G≤Aut(D)是区传递、点本原但非旗传递的.若q＞24√(krk-kr 1)f(这里kr=(k,v-1),q=pf,p是素数,f是正整数),则Soc(G)(≠)E8(q).     

Lie型单群3D4(q)和2-(v,k,1)设计

设D是一个2-(v,k,1)设计,G是D的自同构群.Delandtsheer证明了如果G是区本原的,且D不是射影平面,则G是几乎单群,即存在一个非交换单群T,使得T≤G≤Aut(T).本文证明了T不同构于单群3D4(q),这是区本原设计分类工作的一个不可缺少的组成部分.     

一般投影线性群PGL(2,q)和4-(q+1,5,λ)设计

本文主要考虑了一般投影线性群PGL(2,q)区传递作用下的4-(q+1,5,λ)设计的存在性问题。经讨论知λ的可能值是4。     

二维射影线性群与区传递4-(q+1,5,λ)设计

在组合设计的研究领域中,如何构造具有给定参数的t-设计是一个重要而且困难的问题.利用设计的自同构群来构造t-设计是这一问题有效的解决方法之一.在本文中,设D=(X,B)是一个4-(q+1,5,λ)设计,G≤Aut(D)区传递地作用在D上且X=GF(q)∪{∞},这里GF(q)是q元有限域.设PSL(2,q)(?)G≤PTL(2,q).利用Kramer和Mesner的关于构造区组设计的一个结果和二维射影线性群作用在X的5-子集的集合上的轨道,得到了如下结果:(1)G=PGL(2,17)并且D是一个4-(18,5,4)设计;或(2)G=PSL(2,32)并且D是一个4-(33,5,4)设计;或(3)G=PTL(2,32)并且D是4-(33,5,5)和4-(33,5,20)设计之一.     

Regular (2, 2)-systems

Let (E,I) be an independence system over the finite setE = {e ₁, ,e _n }, whose elements are orderede ₁ e _n . (E,I) is called regular, if the independence of {e _l , ,e _{l k} },l ₁ < <l _k , implies that of {e _{m l} , ,e _{m k} }, wherem _l < ··· <m _k andl ₁ m ₁, ,l _k m _k . (E,I) is called a 2-system, if for anyI I,e E I the setI {e } contains at most 2 distinct circuitsC, C I and the number 2 is minimal with respect to this property. If, in addition, for any two independent setsI andJ the family (C J, C C (J, I)), whereC(J, I) denotes {C C:e J I C {e}}, can be partitioned into 2 subfamilies each of which possesses a transversal, then (E,I) is called a (2, 2)-system. In this paper we characterize regular 2-systems and we show that the classes of regular 2-systems resp. regular (2, 2)-systems are identical.     

Left Euclidean (2, 2)-Algebras

The concept of a commutative and zero-divisor-free Euclidean ring, defined via an Euclidean function, has been generalized to arbitrary left Euclidean rings and than to various other structures as semirings, nearrings and semi-near-rings. As first shown in the dissertation (Hebisch, 1984 Hebisch , U. ( 1984 ). (2, 2)-Algebren mit Euklidischen Algorithmen . Ph.D. thesis, TU Clausthal . [Google Scholar]), these different investigations can be combined considering arbitrary (2, 2)-algebras (S, +, ·), defined as left Euclidean in a suitable way. Here we present and investigate an improved version of this concept. Moreover, Motzkin (1949 Motzkin , T. ( 1949 ). The Euclidean algorithm . Amer. Math. Soc. 55 : 1142 – 1146 . [Google Scholar]) gave a criterion which characterizes a commutative and zero-divisor-free ring as Euclidean by certain chains of product ideals, without the use of Euclidean functions. In the central part of this paper we obtain a corresponding characterization and two further criterions, necessary and sufficient for an algebra (S, +, ·) to be left Euclidean. Based on this we prove several results on these algebras.     

Eine Charakterisierung der zwischenPS-L (2,K) undPGL (2,K) liegenden Permutationsgruppen

Ohne Zusammenfassung     

A proof by graphs that PSL(2, 7) PSL(3, 2)

We give three definitions of the Coxeter graph. By the second one we see that PSL(2, 7) is contained in the automorphism group of that graph as a subgroup of index 2, and by the third one that the same holds for PSL(3, 2).