Maximal Inverse Subsemigroups of the Symmetric Inverse Semigroup on a Finite-Dimensional Vector Space

The notion of “near isomorphism” for torsion-free Abelian groups of finite rank is well known. In particular, this concept turned out to be of importance for classifying almost completely decomposable groups. We extend near isomorphism to classes of torsion-free Abelian groups of infinite rank which are unions of bcd–groups, this is to say unions of groups which are bounded essential extensions of completely decomposable groups. Moreover, we show that nearly isomorphic groups of this class also have nearly isomorphic endomorphism rings considered as Abelian groups.     

Endomorphism Rings of Rigid Almost Completely Decomposable Abelian Groups

A necessary and sufficient condition is found for rigid almost completely decomposable Abelian groups with p-primary regulator quotients to have endomorphism rings isomorphic to those of the corresponding groups with cyclic regulator quotients.     

Schur algebras of Brauer algebras,II

A classical problem of invariant theory and of Lie theory is to determine endomorphism rings of representations of classical groups, for instance of tensor powers of the natural module (Schur–Weyl duality) or of full direct sums of tensor products of exterior powers (Ringel duality). In this article, the endomorphism rings of full direct sums of tensor products of symmetric powers over symplectic and orthogonal groups are determined. These are shown to be isomorphic to Schur algebras of Brauer algebras as defined in Henke and Koenig (Math Z 272(3–4):729–759, 2012). This implies structural properties of the endomorphism rings, such as double centraliser properties, quasi-hereditary, and a universal property, as well as a classification of simple modules.     

On the Determinability of Mixed Abelian Groups by Their Endomorphism Semigroups

Mixed Abelian groups with isomorphic endomorphism semigroups are studied. In particular, the question of when the isomorphism of endomorphism semigroups of Abelian groups implies the isomorphism of the groups themselves is investigated.     

Summability of a ring of endomorphisms of vector groups

Sufficient conditions are found for arbitrary endomorphisms to have a presentation by sum of automorphisms in the class of Abelian groups whose endomorphism rings are isomorphic to a ring of finite-rowed matrices. This result is then used to establish a criterion for such a presentation in terms of type language for vector Abelian groups, whose reduced part does not exceed the first cardinal of nonzero measure. Translated fromAlgebra i Logika, Vol. 37, No. 1, pp. 88–100, January–February, 1998.     

Definability of Abelian groups by homomorphism groups and endomorphism semigroups

In the paper, the isomorphism problem for completely decomposable Abelian torsion-free groups of finite rank is treated under the assumption that the groups of homomorphisms of these groups into some Abelian group are isomorphic and, moreover, the endomorphism semigroups of the groups are isomorphic.     

Modules over discrete valuation domains. II

In the second part of the paper, we study torsion-free modules and mixed modules. We analyze the possibility of the isomorphism of two modules with isomorphic endomorphism rings. We touch on several questions about transitive and fully transitive modules. __________ Translated from Itogi Nauki i Tekhniki, Seriya Sovremennaya Matematika i Ee Prilozheniya. Tematicheskie Obzory. Vol. 122, Algebra, 2006.     

When is an Abelian group isomorphic to its endomorphism group?

In the paper, necessary and sufficient conditions for an Abelian group A to be isomorphic to the endomorphism group End(A) are obtained. The classes of periodic Abelian groups, divisible Abelian groups, nonreduced Abelian groups, and reduced algebraically compact Abelian groups are considered. For certain classes of Abelian groups, the isomorphism problem for a group and its endomorphism group is solved under the assumption that the endomorphism group itself has the corresponding property.     

A counterexample to the reconstruction of <Emphasis Type="Italic">ω</Emphasis>-categorical structures from their endomorphism monoid

We present an example of two countable ω-categorical structures, one of which has a finite relational language, whose endomorphism monoids are isomorphic as abstract monoids, but not as topological monoids—in other words, no isomorphism between these monoids is a homeomorphism. For the same two structures, the automorphism groups and polymorphism clones are isomorphic, but not topologically isomorphic. In particular, there exists a countable ω-categorical structure in a finite relational language which can neither be reconstructed up to first-order biinterpretations from its automorphism group, nor up to existential positive bi-interpretations from its endomorphism monoid, nor up to primitive positive bi-interpretations from its polymorphism clone.     

On Pierce Problem for Reduced <Emphasis Type="Italic">p</Emphasis>-Groups

One of the problems in the study of Abelian groups and their endomorphism rings is the problem of constructing an appropriate structural theory. The structural theorems obtained for Abelian groups and their endomorphism rings allowto reduce the study of complex objects to simpler ones. A radical is one of the tools possessing this property. In this paper, we describe the Jacobson radical of the endomorphism rings of reduced p-groups from some class, which is a solution to the Pierce problem for this class of groups.     

Isomorphism of a Ring to the Endomorphism Ring of an Abelian Group

This paper presents necessary and sufficient conditions under which isomorphism of endomorphism rings of additive groups of arbitrary associative rings with 1 implies isomorphism of these rings. For a certain class of Abelian groups, we present a criterion which shows when isomorphism of their endomorphism rings implies isomorphism of these groups. We demonstrate necessary and sufficient conditions under which an arbitrary ring is the endomorphism ring of an Abelian group. This solves Problem 84 in L. Fuchs’ “Infinite Abelian Groups.”__________Translated from Fundamentalnaya i Prikladnaya Matematika, Vol. 9, No. 1, pp. 231–234, 2003.     

Definability of vector groups by endomorphism semigroups

Some conditions for torsion-free Abelian groups to be isomorphic are found; the groups in question are decomposable into a direct product of rank 1 groups with isomorphic endomorphism semigroups.Translated fromAlgebra i Logika, Vol. 33, No. 4, pp. 422–428, July-August, 1994.     

Isomorphisms of Endomorphism Semigroups of Mixed Abelian Groups

We study abelian groups whose endomorphism rings are rings with unique addition. This means that there exists a unique binary operation of addition on the endomorphism semigroup which turns it into a ring. We also solve some close problems.     

Abelian Groups with Annihilator Ideals of Endomorphism Rings

We describe the periodic groups whose endomorphism rings satisfy the annihilator condition for the principal left ideals generated by nilpotent elements. We prove that torsion-free reduced separable, vector, and algebraically compact groups have endomorphism rings with the annihilator condition for the principal left (right) ideals generated by nilpotent elements if and only if these rings are commutative. We show that the almost injective groups (in the sense of Harada) are injective, i.e. divisible.     

Nil-clean matrix rings

We characterize the nil-clean matrix rings over fields. As a by product, we obtain a complete characterization of the finite rank Abelian groups with nil-clean endomorphism ring and the Abelian groups with strongly nil-clean endomorphism ring, respectively.     

On Purity and Quasiequality of Abelian Groups

We study the Cohn purity in an abelian group regarded as a left module over its endomorphism ring. We prove that if a finite rank torsion-free abelian group G is quasiequal to a direct sum in which all summands are purely simple modules over their endomorphism rings then the module _E(G) G is purely semisimple. This theorem makes it possible to construct abelian groups of any finite rank which are purely semisimple over their endomorphism rings and it reduces the problem of endopure semisimplicity of abelian groups to the same problem in the class of strongly indecomposable abelian groups.     

Finite Tarski algebras are determined by their endomorphisms

We prove that if two finite Tarski algebras have isomorphic endomorphism monoids then they are isomorphic.     

Completely Decomposable Abelian Groups with Clean Endomorphism Rings

Conditions for cleanness of endomorphism rings of completely decomposable Abelian groups are established.     

The endomorphism monoid of a free trioid of rank 1

We describe all endomorphisms of a free trioid of rank 1 and construct a semigroup which is isomorphic to the endomorphism monoid of such free trioid. Also, we give an abstract characteristic for the endomorphism monoid of a free trioid of rank 1 and prove that free trioids are determined by their endomorphism monoids.