Algebras determined by their endomorphism monoids
Almost Butler groups
Generalizing the notion of the almost free group we introduce almost Butler groups. An almost -group of singular cardinality is a -group. Since almost -groups have preseparative chains, the same result in regular cardinality holds under the additional hypothesis that is a -group. Some other results characterizing -groups within the classes of almost -groups and almost -groups are obtained. A theorem of stating that a group of weakly compact cardinality having a -filtration consisting...
Almost completely decomposable groups with primary cyclic regulating quotient
Almost coproducts of finite cyclic groups
A new class of -primary abelian groups that are Hausdorff in the -adic topology and that generalize direct sums of cyclic groups are studied. We call this new class of groups almost coproducts of cyclic groups. These groups are defined in terms of a modified axiom 3 system, and it is observed that such groups appear naturally. For example, is almost a coproduct of finite cyclic groups whenever is a Hausdorff -primary group and is the group of normalized units of the modular group algebra...
Almost free splitters
Let R be a subring of the rationals. We want to investigate self splitting R-modules G, that is, such that . For simplicity we will call such modules splitters (see [10]). Also other names like stones are used (see a dictionary in Ringel’s paper [8]). Our investigation continues [5]. In [5] we answered an open problem by constructing a large class of splitters. Classical splitters are free modules and torsion-free, algebraically compact ones. In [5] we concentrated on splitters which are larger...
Almost totally projective groups
Almost-flat modules
We present general properties for almost-flat modules and we prove that a self-small right module is almost flat as a left module over its endomorphism ring if and only if the class of -static modules is closed under the kernels.
Almost-free E(R)-algebras and E(A,R)-modules
Let R be a unital commutative ring and A a unital R-algebra. We introduce the category of E(A,R)-modules which is a natural extension of the category of E-modules. The properties of E(A,R)-modules are studied; in particular we consider the subclass of E(R)-algebras. This subclass is of special interest since it coincides with the class of E-rings in the case R = ℤ. Assuming diamond ⋄, almost-free E(R)-algebras of cardinality κ are constructed for any regular non-weakly compact cardinal κ > ℵ...
An addendum and corrigendum to "Almost free splitters" (Colloq. Math. 81 (1999), 193-221)
Let R be a subring of the rational numbers ℚ. We recall from [3] that an R-module G is a splitter if . In this note we correct the statement of Main Theorem 1.5 in [3] and discuss the existence of non-free splitters of cardinality ℵ₁ under the negation of the special continuum hypothesis CH.
An Addition Theorem in a Finite Abelian Group.
An algebraic characterization of multiplicative semigroups of real valued functions.
An alternative proof of Hill's criterion of freeness for Abelian groups.
An axiomatic approach for the Hajós theorem.
An extension of Zassenhaus' theorem on endomorphism rings
Let R be a ring with identity such that R⁺, the additive group of R, is torsion-free. If there is some R-module M such that and , we call R a Zassenhaus ring. Hans Zassenhaus showed in 1967 that whenever R⁺ is free of finite rank, then R is a Zassenhaus ring. We will show that if R⁺ is free of countable rank and each element of R is algebraic over ℚ, then R is a Zassenhaus ring. We will give an example showing that this restriction on R is needed. Moreover, we will show that a ring due to A....
An improvement on Olson's constant for ℤₚ ⊕ ℤₚ
An orthogonal theory of a set-valued bifunctor
Analytic and arithmetic theory of semigroups with divisor theory
A-Rings
A ring R is called an E-ring if every endomorphism of R⁺, the additive group of R, is multiplication on the left by an element of R. This is a well known notion in the theory of abelian groups. We want to change the "E" as in endomorphisms to an "A" as in automorphisms: We define a ring to be an A-ring if every automorphism of R⁺ is multiplication on the left by some element of R. We show that many torsion-free finite rank (tffr) A-rings are actually E-rings. While we have an example of a mixed...
Arithmetic of block monoids
Arithmetic of stabilizers of ideals in group rings.