Minkowski－Farkas引理和Stiemke引理的拓广

本又把Ｗｅａｋｌｙａｒｂｉｔｒａｇｅ－ｆｒｅｅ和Ｓｔｒｉｅｄｙａｒｂｉｔｒａｇｅ－ｆｒｅｅ从Ｅａｄｉｄｅａｎ空间拓广到无限维空间，从而得到拓广的Ｍｉｎｋｏｗｓｋｉ－Ｆａｒｋａｓ引理和Ｓｔｉｅｍｋｅ引理．     

A combinatorial proof of the Removal Lemma for Groups

Green [B. Green, A Szemerédi-type regularity lemma in abelian groups, with applications, Geom. Funct. Anal. 15 (2005) 340-376] established a version of the Szemerédi Regularity Lemma for abelian groups and derived the Removal Lemma for abelian groups as its corollary. We provide another proof of his Removal Lemma that allows us to extend its statement to all finite groups. We also discuss possible extensions of the Removal Lemma to systems of equations.     

关于Morse引理的推广

Morse Lemma是奇点理论中一个极为重要的结论。[1]的作者称其文中的定理1和定理2是Morse Lemma的推广。为此我们愿就[1]中的几个问题与[1]的作者商榷。     

A sharp Schwarz inequality on the boundary

A number of classical results reflect the fact that if a holomorphic function maps the unit disk into itself, taking the origin into the origin, and if some boundary point maps to the boundary, then the map is a magnification at . We prove a sharp quantitative version of this result which also sharpens a classical result of Loewner.

     

On a surprising covariance identity

This paper deals with the fact that the covariance of the integer and fractional parts of a sum of n random numbers chosen independently and randomly on (0,1) is- 1/12, for all n >2. While the result is of interest, it is the three different ways proposed to arrive at the result that are particularly instructive. These proofs highlight the usefulness of: (i) different results in elementary probability, and (ii) computational techniques, which are also of interest on their own.     

Proof of a tiling conjecture of Komlós

A conjecture of Komlós states that for every graph H, there is a constant K such that if G is any n‐vertex graph of minimum degree at least (1 ? (1/χ_cr(H)))n, where χ_cr(H) denotes the critical chromatic number of H, then G contains an H‐matching that covers all but at most K vertices of G. In this paper we prove that the conjecture holds for all sufficiently large values of n. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 23: 180–205, 2003     

Effective Borel degrees of some topological functions

The focus of this paper is the incomputability of some topological functions (with respect to certain representations) using the tools of Borel computability theory, as introduced by V. Brattka in [3] and [4]. First, we analyze some basic topological functions on closed subsets of ?ⁿ , like closure, border, intersection, and derivative, and we prove for such functions results of Σ⁰₂‐completeness and Σ⁰₃‐completeness in the effective Borel hierarchy. Then, following [13], we re‐consider two well‐known topological results: the lemmas of Urysohn and Urysohn‐Tietze for generic metric spaces (for the latter we refer to the proof given by Dieudonné). Both lemmas define Σ⁰₂‐computable functions which in some cases are even Σ⁰₂‐complete. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On Lelong-Bremermann Lemma

The main theorem of this note is the following refinement of the well-known Lelong-Bremermann Lemma:

Let be a continuous plurisubharmonic function on a Stein manifold of dimension Then there exists an integer , natural numbers , and analytic mappings such that the sequence of functions

converges to uniformly on each compact subset of .

In the case when is a domain in the complex plane, it is shown that one can take in the theorem above (Section 3); on the other hand, for -circular plurisubharmonic functions in the statement of this theorem is true with (Section 4). The last section contains some remarks and open questions.

     

Categorical abstract algebraic logic: The Diagram and the Reduction Operator Lemmas

The study of structure systems, an abstraction of the concept of first‐order structures, is continued. Structure systems have algebraic systems as their algebraic reducts and their relational component consists of a collection of relation systems on the underlying functors. An analog of the expansion of a first‐order structure by constants is presented. Furthermore, analogs of the Diagram Lemma and the Reduction Operator Lemma from the theory of equality‐free first‐order structures are provided in the framework of structure systems. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the Pósa-Seymour conjecture

Paul Seymour conjectured that any graph G of order n and minimum degree at least contains the k^th power of a Hamilton cycle. We prove the following approximate version. For any ϵ ≥ 0 and positive integer k, there is an n₀ such that, if G has order n ≥ n₀ and minimum degree at least $(\frac{k}{k+1} + \epsilon )n$, then G contains the k^th power of a Hamilton cycle. © 1998 John Wiley & Sons, Inc. J. Graph Theory 29: 167–176, 1998     

A multilinear Phelps' Lemma

We prove a multilinear version of Phelps' Lemma: if the zero sets of multilinear forms of norm one are `close', then so are the multilinear forms.

     

Revisit the Lovász Local Lemma

We provide a sufficient condition for showing that the probability of none of the events A ₁, A ₂,...,A _n occurs is positive. This condition explicitly involves the dependency digraph and the probabilities of the A _i's. Some applications are given.     

Minimum degree thresholds for bipartite graph tiling

Given a bipartite graph H and a positive integer n such that v(H) divides 2n, we define the minimum degree threshold for bipartite H‐tiling, δ₂(n, H), as the smallest integer k such that every bipartite graph G with n vertices in each partition and minimum degree δ(G)≥k contains a spanning subgraph consisting of vertex‐disjoint copies of H. Zhao, Hladký‐Schacht, Czygrinow‐DeBiasio determined δ₂(n, K_{s, t}) exactly for all s?t and suffi‐ciently large n. In this article we determine δ₂(n, H), up to an additive constant, for all bipartite H and sufficiently large n. Additionally, we give a corresponding minimum degree threshold to guarantee that G has an H‐tiling missing only a constant number of vertices. Our δ₂(n, H) depends on either the chromatic number χ(H) or the critical chromatic number χ_cr(H), while the threshold for the almost perfect tiling only depends on χ_cr(H). These results can be viewed as bipartite analogs to the results of Kuhn and Osthus [Combinatorica 29 (2009), 65–107] and of Shokoufandeh and Zhao [Rand Struc Alg 23 (2003), 180–205]. © 2011 Wiley Periodicals, Inc. J Graph Theory     

On Theorem of the “Mountain Impasse” Type

ＬｅｔＦ（ｕ），Ｇ（ｕ）ｂｅＣ１－ｆｕｎｃｔｉｏｎａｌｓｏｎａＨｉｌｂｅｒｔｓｐａｃｅＨａｎｄｓｕｐｕ∈ＨＦ（ｕ）＝∞．ＬｅｔＫｂｅａｃｏｍｐａｃｔｍｅｔｒｉｃｓｐａｃｅａｎｄｌｅｔＫｂｅａｎｏｎ－ｅｍｐｔｙｃｌｏｓｅｄｓｕｂｓｅｔ≠Ｋ，ｐ∈Ｃ（Ｋ；Ｈ）．ＤｅｎｏｔｅＦＲ＝｛ｕ∈Ｈ｜Ｆ（ｕ）Ｒ｝；　　　　　　ΦＲ＝｛ｐ∈Ｃ（Ｋ；ＦＲ）｜ｐ＝ｐｏｎＫ｝；ｃ（Ｒ）＝ｉｎｆｐ∈ΦＲｍａｘξ∈ＫＧ（ｐ（ξ））；ｃ０＝ｍａｘξ∈ＫＧ（ｐ（ξ））；Φ∞＝｛ｐ∈Ｃ（Ｋ；Ｈ）｜ｐ＝ｐｏｎＫ｝；…     

Multipartite Ramsey numbers for odd cycles

In this paper we study multipartite Ramsey numbers for odd cycles. We formulate the following conjecture: Let n≥5 be an arbitrary positive odd integer; then, in any two‐coloring of the edges of the complete 5‐partite graph K((n?1)/2, (n?1)/2, (n?1)/2, (n?1)/2, 1) there is a monochromatic C_n, a cycle of length n. This roughly says that the Ramsey number for C_n (i.e. 2n?1 ) will not change (somewhat surprisingly) if four large “holes” are allowed. Note that this would be best possible as the statement is not true if we delete from K_2n?1 the edges within a set of size (n+ 1)/2. We prove an approximate version of the above conjecture. © 2009 Wiley Periodicals, Inc. J Graph Theory 61:12‐21, 2009     

一类具有对称性的非线性微分方程的正值同宿轨道

利用变分逼近方法，证明了二阶非线性微分方程ue(t)-a(t)u(t) f(t,u(t))=0存在惟一的正值同宿轨道，其中a(t)和f(t,u)都是关于变量t的偶函数。     

Regularity of solutions to scalar conservation laws with a force

We prove regularity estimates for entropy solutions to scalar conservation laws with a force. Based on the kinetic form of a scalar conservation law, a new decomposition of entropy solutions is introduced, by means of a decomposition in the velocity variable, adapted to the non-degeneracy properties of the flux function. This allows a finer control of the degeneracy behavior of the flux. In addition, this decomposition allows to make use of the fact that the entropy dissipation measure has locally finite singular moments. Based on these observations, improved regularity estimates for entropy solutions to (forced) scalar conservation laws are obtained.     

A Note on a Matrix Version of the Farkas Lemma

A linear polyomial non-negative on the non-negativity domain of finitely many linear polynomials can be expressed as their non-negative linear combination. Recently, under several additional assumptions, Helton, Klep, and McCullough extended this result to matrix polynomials. The aim of this article is to study which of these additional assumptions are really necessary.