A note on the commutativity of groups

In this article, we show that a group is abelian if and only if every two elements of the same order commute.     

A minimal pair joining to a plus cupping Turing degree

A computably enumerable (c.e.) degree a is called nonbounding, if it bounds no minimal pair, and plus cupping, if every nonzero c.e. degree x below a is cuppable. Let NB and PC be the sets of all nonbounding and plus cupping c.e. degrees, respectively. Both NB and PC are well understood, but it has not been possible so far to distinguish between the two classes. In the present paper, we investigate the relationship between the classes NB and PC , and show that there exists a minimal pair which join to a plus cupping degree, so that PC ? NB . This gives a first known difference between NB and PC . (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A class of finite groups with complete character degree graphs

In this paper, we construct a new class of finite groups whose common divisor graphs are complete graphs, while there is no prime dividing all the nontrivial degrees.     

基于相似度的样本分类算法

结合粗糙集理论中相似关系的思想,提出了一种基本相似度的样本分类算法.并通过实例说明了该分类算法的有效性。     

A topological characterization of consistency of logic theories in propositional logic

The main purpose of this note is to characterize consistency of logic theories in propositional logic by means of topological concept. Based on the concepts of truth degree of formulas and similarity degree between formulas the concept of logic metric space has been proposed by the first author. It is proved in this note that a closed logic theory Γ is consistent if and only if it contains no interior point in the logic metric space. Moreover the relationship between logic closedness and topological closedness of a logic theory Γ is discussed. Finally, the concept of full divergency is also characterized by means of the topological concept of density. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

从球面到紧致光滑流形的连续映射

本文研究了球面到紧致光滑流形的连续映射的性质.利用Brouwer映射度理论和微分拓扑的基本方法,得到了Munkholm型定理.     

A system of coupled pendulii

We study the existence of solutions for a coupled system of n-dimensional pendulum equations under generalized periodic-type conditions. We obtain existence results under appropriate conditions using topological degree methods and a shooting type argument.     

平衡二部图的四圈覆盖

对任意的正整数ｋ,如果每部２ｋ个点的平衡二部图Ｇ＝（ｖ１,ｖ２;Ｅ）的最小度大于等于４ｋ／３,那么Ｇ恰好被ｋ个相互独立的四圈覆盖。     

A new degree bound for invariant rings

In this paper we give a new degree bound for polynomial invariant rings of finite groups and give some applications.

     

无向图可迹的一个充分条件

无向图G是简单连通图,且最小度为δ.如果G中包含一条生成路,则G是可迹的.无向图G的叶子数L(G)是G中生成树所含的叶子数的最大数.基于L(G)和δ,证明了一个充分条件使得无向图G是可迹的,即设G为连通图,最小度为δ≤4.若δ≥(1/2)(L(G)+2),G是可迹的.