Strong ergodic theorems for commutative semigroups of operators

We prove strong mean convergence theorems and the existence of ergodic projection and retraction for commutative semigroups of operators which is Eberlein-weakly almost periodic.

     

Hilbert空间中渐近殆非扩张曲线的强遍历收敛定理

设C为Hilbert空间H的非空子集，G为一个交换半群．文中定义了G上渐近殆非扩张曲线“（·）：G→C，证明了渐近殆非扩张曲线的强遍历收敛定理．应用于半群，得到了在失去凸性的情况下，渐近非扩张型半群的殆轨道的强遍历收敛定理．推广和改进了以前所有的结果。     

Computing finite commutative semigroups: Part II

New precedence results are obtained for semigroups with zero, which describe the first non-zero row in detail and provide effective comparisons with subsequent rows. These results are used to further sharpen existing algorithms for the computation of finite commutative semigroups, confirm the number of distinct commutative semigroups of order 9, and determine the number of distinct commutative semigroups of order 10.     

The structure of commutative semigroups with the ideal extension property

In this paper, we will characterize commutative semigroups which have the ideal extension property (IEP). This characterization describes the multiplicative structure of commutative semigroups with IEP. Establishing this characterization was motivated not only by an interest in IEP itself, but also by the fact that in the category of commutative semigroups, the congruence extension property (CEP) implies IEP. A few preliminary results which hold in the general (non-commutative) case are discussed below. Following these initial observations, all semigroups considered are commutative.     

交换半群的强半格

本文刻划交换半群的强半格上的最小半格同余，并证明由此得到的商半群为对应的每个交换半群的商半群的强半格。     

Computing finite commutative semigroups

Precedence results are used to improve existing algorithms for the enumeration of finite commutative semigroups. As an application 11,545,843 distinct commutative semigroups of order 9 were found.     

Subdirect decompositions of finitely generated commutative semigroups

All finitely generated commutative semigroups which do not have proper finite subdirect decompositions are determined. This yields subdirect decompositions of finitely generated commutative semigroups and some idea of their structure.     

关于交换序半群的一个注记

给出了正则交换序半群的与素理想结构有关的若干性质，还给出了为有限个主理想的并的交换序半群类中的诺特性，阿基米德性，正则性以及有限生成性之间的一些关系。     

Presentations for subsemigroups of finitely generated commutative semigroups

We introduce the concept of presentation for subsemigroups of finitely generated commutative semigroups, which extends the concept of presentation for finitely generated commutative semigroups. We show that for every subsemigroup of a finitely generated commutative semigroup there are special presentations which solve the word problem in the given subsemigroup. Some properties like being cancellative, reduced and/or torsion free are studied under this new point of view. This paper was supported by the project DGES PB96-1424.     

关于弱交换PO—半群中的一个问题

本文引入弱交换ｐｏ－半群的概论２，研究这类半群到Ａｒｃｈｉｍｅｄｅａｎ子半群的半格分解，得到了这半群类似于具平凡序的弱交换半群的一个特征，由此在更一般的情形下回答了Ｋｅｈａｙｏｐｕｌｕ在「１」中提出的一个问题，并作为推论得到弱交换ｐｏｅ－半群和具平凡序的弱交换半群的已知结果。     

A construction of commutative nilsemigroups

All commutative nilsemigroups are constructed from congruences on free commutative semigroups.     

关于弱交换po－半群

在本文中我们引入弱交换ｐｏ－半群的概念，并研究这类半群到其Ａｒｃｈｉｍｅｄｅｓ子半群的半格分解，给出了这类半群类似于无序半群相应结果的一个刻画。作为推论，我们得到弱交换ｐｏｅ－群和无序半群的相应刻画。     

交换矩阵半群的可约性

首先分别给出单生矩阵半群或者摹群不可约、不可分解以及完全可约的充分必要条件,其次讨论一般域上矩阵半群的可约性的一些条件,最后特别地讨论实数域上矩阵半群的可约性,完全确定了实数域上对称和反对称矩阵组成的不可约交换矩阵半群.     

Principal ideals of finitely generated commutative monoids

We study the semigroups isomorphic to principal ideals of finitely generated commutative monoids. We define the concept of finite presentation for this kind of semigroups. Furthermore, we show how to obtain information on these semigroups from their presentations.     

Varieties and Nilpotent Extensions of Permutative Periodic Semigroups

We investigate certain semigroup varieties formed by nilpotent extensions of orthodox normal bands of commutative periodic groups. Such semigroups are shown to be both structurally periodic and structurally commutative, and are therefore structurally inverse semigroups. Such semigroups are also shown to be dense semilattices of structurally group semigroups. Making use of these structure decompositions, we prove that the subvariety lattice of any variety comprised of such semigroups is isomorphic to the direct product of the following three sublattices: its sublattice of all structurally trivial semigroup varieties, its sublattice of all semilattice varieties, and its sublattice of all group varieties. We conclude, therefore, that to completely describe this lattice, we must first describe completely the lattice of all structurally trivial semigroup varieties, since the other two are well known lattices.     

Finite union of commutative power joined semigroups

A commutative semigroup is called power joined if for every element a, b there are positive integers m, n such that a^m=bⁿ. A commutative power joined semigroup is archimedean (p. 131, [3]) and cannot be decomposed into the disjoint union of more than one subsemigroup. Every commutative semigroup is uniquely decomposed into the disjoint union of power joined subsemigroups which are called the power joined components. This paper determines the structure of commutative archimedean semigroups which have a finite number of power joined components. The number of power joined components of commutative archimedean semigroups is one or three or infinity. The research for this paper was supported in part by NSF Grant GP-11964.     

可交换的双单E-半群

具体地描述了双单E-半群上的任意两个同余是可交换,给出了任意两个同余可交换的充要条件.     

Semigroups of order 8

We construct all non-equivalent semigroups of order 8, obtain their total number, and specify commutative semigroups, regular semigroups and inverse semigroups among them. And we present their classification with respect to the equivalences of the Green’s relations, that is, egg-box types with information about the positions of idempotent elements in them.     

几类亚交换序半群

本文研究几类亚交换序半群的性质,并将具有单位元的亚交换序半群的一些结果扩张到这几类亚交换序半群上,使得这些结果更加细化,其中主要证明了以下定理：伪交换序半群可以分解成阿基米德序半群的半格．并且,一般来说,这种分解不是唯一的．     

Definability in the lattice of equational theories of commutative semigroups

In this paper we study first-order definability in the lattice of equational theories of commutative semigroups. In a series of papers, J. Jezek, solving problems posed by A. Tarski and R. McKenzie, has proved, in particular, that each equational theory is first-order definable in the lattice of equational theories of a given type, up to automorphism, and that such lattices have no automorphisms besides the obvious syntactically defined ones (with exceptions for special unary types). He has proved also that the most important classes of theories of a given type are so definable. In a later paper, Jezek and McKenzie have ``almost proved" the same facts for the lattice of equational theories of semigroups. There were good reasons to believe that the same can be proved for the lattice of equational theories of commutative semigroups. In this paper, however, we show that the case of commutative semigroups is different.