Fold‐2‐covering triangular embeddings

For a graph G and a positive integer m, G_(m) is the graph obtained from G by replacing every vertex by an independent set of size m and every edge by m² edges joining all possible new pairs of ends. If G triangulates a surface, then it is easy to see from Euler's formula that G_(m) can, in principle, triangulate a surface. For m prime and at least 7, it has previously been shown that in fact G_(m) does triangulate a surface, and in fact does so as a “covering with folds” of the original triangulation. For m = 5, this would be a consequence of Tutte's 5‐Flow Conjecture. In this work, we investigate the case m = 2 and describe simple classes of triangulations G for which G₍₂₎ does have a triangulation that covers G “with folds,” as well as providing a simple infinite class of triangulations G of the sphere for which G₍₂₎ does not triangulate any surface. © 2003 Wiley Periodicals, Inc. J Graph Theory 43: 79–92, 2003     

Products of foldable triangulations

Regular triangulations of products of lattice polytopes are constructed with the additional property that the dual graphs of the triangulations are bipartite. The (weighted) size difference of this bipartition is a lower bound for the number of real roots of certain sparse polynomial systems by recent results of Soprunova and Sottile [E. Soprunova, F. Sottile, Lower bounds for real solutions to sparse polynomial systems, Adv. Math. 204 (1) (2006) 116–151]. Special attention is paid to the cube case.     

闭模糊n级正关联理想

引入闭模糊n级正关联理想 ,刻划其结构和性质。     

Toric Initial Ideals of Δ-Normal Configurations: Cohen-Macaulayness and Degree Bounds

A normal (respectively, graded normal) vector configuration\({\cal A}\) defines the toric ideal \({I}_{\cal A}\) of a normal (respectively, projectively normal) toric variety. These ideals are Cohen-Macaulay, and when \({\cal A}\) is normal and graded, \({I}_{\cal A}\) is generated in degree at most the dimension of \({I}_{\cal A}\). Based on this, Sturmfels asked if these properties extend to initial ideals—when \({\cal A}\) is normal, is there an initial ideal of \({I}_{\cal A}\) that is Cohen-Macaulay, and when \({\cal A}\) is normal and graded, does \({I}_{\cal A}\) have a Gröbner basis generated in degree at most dim(\({I}_{\cal A}\)) ? In this paper, we answer both questions positively for Δ-normal configurations. These are normal configurations that admit a regular triangulation Δ with the property that the subconfiguration in each cell of the triangulation is again normal. Such configurations properly contain among them all vector configurations that admit a regular unimodular triangulation. We construct non-trivial families of both Δ-normal and non-Δ-normal configurations.     

实二次域上正定偶幺模格的类数

本文综合利用邻格方法及Siegel　mass公式证明了实二次域Q( )上 内的偶幺模 格类数为2当且仅当Q( ),n=4及Q( ).n=8.     

t-Spread strongly stable monomial ideals*

We introduce the concept of t-spread monomials and t-spread strongly stable ideals. These concepts are a natural generalization of strongly stable and squarefree strongly stable ideals. For the study of this class of ideals we use the t-fold stretching operator. It is shown that t-spread strongly stable ideals are componentwise linear. Their height, their graded Betti numbers and their generic initial ideal are determined. We also consider the toric rings whose generators come from t-spread principal Borel ideals.     

Hamilton李超代数的Borel子代数

设H(n)(n≥5)为复数域上秩为n的有限维Hamilton单李超代数.通过对正则元的分类,得到H(n)(n=5,6,7)关于典范环面的所有正根系,从而通过确定单根系得到正根系的连接关系,进而得到所有的Borel子代数及其连接关系.证明了H(n)(n≥5)的所有Borel子代数都不是极大可解的子代数.     

典型根系中不可约子根系的数目

Let Ф be an irreducible root system of classical type. In this short note, we study the irreducible subsystems of Ф and compute the number of irreducible subsystems of any rank k in Ф.     

Shifting Operations and Graded Betti Numbers

The behaviour of graded Betti numbers under exterior and symmetric algebraic shifting is studied. It is shown that the extremal Betti numbers are stable under these operations. Moreover, the possible sequences of super extremal Betti numbers for a graded ideal with given Hilbert function are characterized. Finally it is shown that over a field of characteristic 0, the graded Betti numbers of a squarefree monomial ideal are bounded by those of the corresponding squarefree lexsegment ideal.     

四次函数实零点的完全判据和正定条件

本文给出了四次函数实零点的完全判据和正定条件,这一结果在研究多项式系统的奇点分析和分支问题时给出了可以实用的判据．     

Z[(1 21~(1/2))/2]上正定幺模格的分类(英文)

本文综合利用邻格方法及Siegelmass公式对Z[(1 2 1) /2 ]上秩 4的正定幺模格实现了分类 ,得到了gen(I4 )的类数为 9,偶模格的类数为 3,并且给了代表格     

BCK-代数的Ω-模糊正定关联理想

给定一个集合Ω,引入了BCK-代数的Ω-模糊正定关联理想的概念,给出了一些恰当的例子,讨论了BCK-代数的Ω-模糊理想与Ω-模糊正定关联理想的关系.利用模糊正定关联理想,刻画了Ω-模糊正定关联理想.反之,模糊正定关联理想通过Ω-模糊正定关联理想来构造.证明了Ω-模糊正定关联理想(Ω-模糊理想)的同态原象仍是Ω-模糊理想(Ω-模糊理想).     

Competitive equilibrium on risk exchanges: A constrained market approach

This paper concerns competitive equilibria on a market for risk exchanges (rex). Initially a short resume is offered of some fundamental results obtained in this field and essentially due to K. Borch. Much attention is devoted to the key question that equilibria could be seen as generated by a market working for contingent coverings (shortly an analytic approach) or by a simpler market for risks governed by a synthetic premium principle. The idea of rex markets constrained both on the quantity side as well as for the tarification system applied is then introduced as a useful tool to study e.g. markets where unconstrained equilibria turn out too complex. Finally an example of a non-traditional constrained market is briefly discussed.     

Arithmetic Continuation of Regular Roots of Formal Parametric Polynomial Systems

Given a regular system of polynomial equations with power series coefficients, an initial root is continued as a power series. With the ground domain as an arbitrary field, arithmetic alone is used for the root continuation over this field, and computation is quadratic in the number of computed coefficients. If the power series of the coefficients of the polynomial are geometrically bounded, then the coefficients of the power series of the root are also.     

关于正线性方程组正解的判定定理

给出正线性方程组正解的概念,给出并证明了正线性方程组正解的若干判别方法,对教学有一定的指导意义.