对偶根和F.A.SZSZ问题21

本文证明了根 R 的补根是由所有非 R-半单的亚直既约环确定的上根.对半遗传根,给出了补根的进一步刻划,证明了遗传根是对偶根,当且仅当它是由一个亚直既约环环类确定的上根,每个遗传对偶根或者是超幂零的,或者是次幂等的.     

对偶根和F.A.SZSZ问题21

本文证明了根 R 的补根是由所有非 R-半单的亚直既约环确定的上根.对半遗传根,给出了补根的进一步刻划,证明了遗传根是对偶根,当且仅当它是由一个亚直既约环环类确定的上根,每个遗传对偶根或者是超幂零的,或者是次幂等的.     

J-半单亚直既约环类确定的上限

Ｆ．Ａ．Ｓｚａｓｚ在［１］中提出公开问题５５：设Ｋ是Ｊａｃｏｂｓｏｎ根为零的全体亚直既约环类,研究类Ｋ确定的上根．本文对此进行了研究,证明了Ｊａｃｏｂｓｏｎ根为零的全体亚直既约环类Ｋ确定的上根Ｒ是特殊根,它介于Ｊａｃｏｂｓｏｎ根与Ｂｒｏｗｎ－ＭｃＣｏｙ根之间．并给出任意结合环Ａ为Ｒ－根环的充要条件．     

σ-根与σ-半单类的构造

继［１～３］分别给出σ－根及其半单类的两个特征性质，研究了对于已知环类Ｍ，含于Ｍ的最大σ－根及σ－半单类和包含Ｍ的最小σ－半单类的构造，同时得到σ－半单闭包σ－遗传的一个充分条件．     

半单算子与半单类

1981年,W.G.Leavitt 深入地讨论了上根算子与根环类之间的关系(文〔1〕).但对于半单算子尚未见文献论述。本文考察了任一环类在半单算子作用下的状况。文中引进的(?)-可半单类在某种意义下可认为是〔1〕中 r-类的对偶;给出了(?)可半单类的刻划并利用上正则类考察了下根 L(M)的半单类。文中还给出半单算子作用下的环类 (?)M 成为遗传根和超幂零根的半单类的充要条件;得到了 U(?)M 是超幂零根的一个充分条件。     

环的半单算子与半单类

设M是任意环类,u,ψ分别表示上根算子及半单算子。W.G.Leavitt在[1]中研究了uM成为遗传根的充要条件。本文将讨论ψM成为半单类,本质闭类,同态闭类或具有其它环类性质的一些等价条件。作为推论,最后给     

代数正规类中的遗传根与强半单根

Puczylowski建立了一般代数对象类的根理论.本文在代数正规类中,用格论方法刻划一般遗传根和强半单根类,探究它们的一些性质,推广了已知各类代数系统的某些根论研究.     

群的遗传根性和强半单根性

本文利用群的根性的性质,解决了Szasz在环的根性理论中提出的公开问题在群论中的对应问题.同时我们研究了群的遗传根性和强半单根性的一些性质,并介绍了群的根类的交运算和并运算,由此得到了一些很好的结果.     

模的结构

本文引进了投射根、半自反根概念,讨论了亚投射性、半自反性和无挠性之间的关系,并对环进行了分类。     

半环的Jacobson关系根与Jacobson根

Bourno与Zassenhaus, Lizuka分别定义了半环的Jacobson根。但是刻划关于这种根的半单类的最好结果是LaTorre所证明的,Jacobson根为零的半环“半同构”于本原半环的亚直和。本文将以定义在半环上的几类特殊的等价关系为基础,来探讨任     

A note on residually small varieties of semigroups

It is proved for any varietyG of groups that if the subdirectly irreducible groups inG form a set, and if the subdirectly irreducible representation algebras of groups inG form a set, then every finite group inG is Abelian. The result is essential for the characterization of residually finite varieties of semigroups.     

分次环，A，Aｅ和Smash积A＃G*是亚直既约环的条件

讨论了分次环Ａ，Ａ_ｅ和Ａ＃Ｇ^*的相关性质，在Ａ是分次忠实时，Ａ＃Ｇ^*是亚直既约环当且仅当Ａ_ｅ是亚直既约环；在Ａ是分次非退化时，Ａ＃Ｇ^*是Ｇ亚直既约环当且仅当Ａ是分次亚直既约环．     

Subdirectly irreducible commutative multiplicatively idempotent semirings

Commutative multiplicatively idempotent semirings were studied by the authors and F. ?vr?ek, where the connections to distributive lattices and unitary Boolean rings were established. The variety of these semirings has nice algebraic properties and hence there arose the question to describe this variety, possibly by its subdirectly irreducible members. For the subvariety of so-called Boolean semirings, the subdirectly irreducible members were described by F. Guzmán. He showed that there were just two subdirectly irreducible members, which are the 2-element distributive lattice and the 2-element Boolean ring. We are going to show that although commutative multiplicatively idempotent semirings are at first glance a slight modification of Boolean semirings, for each cardinal n > 1, there exist at least two subdirectly irreducible members of cardinality n and at least 2ⁿ such members if n is infinite. For \({n \in \{2, 3, 4\}}\) the number of subdirectly irreducible members of cardinality n is exactly 2.     

Subdirectly irreducible algebras with hyperidentities of the variety of De Morgan algebras

The paper characterizes the class of subdirectly irreducible algebras satisfying hyperidentities of the variety of De Morgan algebras. Such algebras are called subdirectly irreducible De Morgan quasilattices. The suggested characterization is quite close to that of the classical case of subdirectly irreducible DeMorgan algebras.     

Ultraproducts preserve finite subdirect reducibility

An algebraic structure A is said to be finitely subdirectly reducible if A is not finitely subdirectly irreducible. We show that for any signature providing only finitely many relation symbols, the class of finitely subdirectly reducible algebraic structures is closed with respect to the formation of ultraproducts. We provide some corollaries and examples for axiomatizable classes that are closed with respect to the formation of finite subdirect products, in particular, for varieties and quasivarieties.     

Some subdirectly irreducible idempotent semigroups

Subdirectly irreducible idempotent semigroups were characterized in [3], and in that paper, their connection with the various equational classes of idempotent semigroups was discussed. All these results are in terms of identities, so that examples of subdirectly irreducibles in the equational classes are explicitly known only for small classes. It is easy to show from general considerations (see the last section of the present paper) that every proper equational subclass of the class of idempotent semigroups is generated (as an equational class) by one or two subdirectly irreducibles. In this paper we give an example of a subdirectly irreducible for each join irreducible equational class of idempotent semigroups, which generates the class. This list, together with known results, gives explicit examples of one or two finite subdirectly irreducibles which generate the various equational classes. Research supported by the National Research Council of Canada.     

On idempotent modifications of generalized <Emphasis Type="Italic">MV</Emphasis>-algebras

The notion of idempotent modification of an algebra was introduced by Je?ek; he proved that the idempotent modification of a group is always subdirectly irreducible. In the present note we show that the idempotent modification of a generalized MV -algebra having more than two elements is directly irreducible if and only if there exists an element in A which fails to be boolean. Some further results on idempotent modifications are also proved.     

Semi-Nelson Algebras

Generalizing the well known and exploited relation between Heyting and Nelson algebras to semi-Heyting algebras, we introduce the variety of semi-Nelson algebras. The main tool for its study is the construction given by Vakarelov. Using it, we characterize the lattice of congruences of a semi-Nelson algebra through some of its deductive systems, use this to find the subdirectly irreducible algebras, prove that the variety is arithmetical, has equationally definable principal congruences, has the congruence extension property and describe the semisimple subvarieties.     

幂等扩张的有界分配格

考察了扩张的有界分配格类eD即带有自同态k的有界分配格,研究了具有幂等性的eD-代数的表示、同余关系以及次直不可约性,证明了这样的代数类有5个互不同构的次直不可约的幂等扩张的有界分配格。