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A canonical directly infinite ring

Mario Petrich, Pedro V. Silva (2001)

Czechoslovak Mathematical Journal

Let be the set of nonnegative integers and the ring of integers. Let be the ring of N × N matrices over generated by the following two matrices: one obtained from the identity matrix by shifting the ones one position to the right and the other one position down. This ring plays an important role in the study of directly finite rings. Calculation of invertible and idempotent elements of yields that the subrings generated by them coincide. This subring is the sum of the ideal consisting of...

A direct factor theorem for commutative group algebras

William Ullery (1992)

Commentationes Mathematicae Universitatis Carolinae

Suppose F is a field of characteristic p 0 and H is a p -primary abelian A -group. It is shown that H is a direct factor of the group of units of the group algebra F H .

A Survey of Rings Generated by Units

Ashish K. Srivastava (2010)

Annales de la faculté des sciences de Toulouse Mathématiques

This article presents a brief survey of the work done on rings generated by their units.

Algebraic analysis in structures with the Kaplansky-Jacobson property

D. Przeworska-Rolewicz (2005)

Studia Mathematica

In 1950 N. Jacobson proved that if u is an element of a ring with unit such that u has more than one right inverse, then it has infinitely many right inverses. He also mentioned that I. Kaplansky proved this in another way. Recently, K. P. Shum and Y. Q. Gao gave a new (non-constructive) proof of the Kaplansky-Jacobson theorem for monoids admitting a ring structure. We generalize that theorem to monoids without any ring structure and we show the consequences of the generalized Kaplansky-Jacobson...

Basic subgroups in abelian group rings

Peter Vassilev Danchev (2002)

Czechoslovak Mathematical Journal

Suppose R is a commutative ring with identity of prime characteristic p and G is an arbitrary abelian p -group. In the present paper, a basic subgroup and a lower basic subgroup of the p -component U p ( R G ) and of the factor-group U p ( R G ) / G of the unit group U ( R G ) in the modular group algebra R G are established, in the case when R is weakly perfect. Moreover, a lower basic subgroup and a basic subgroup of the normed p -component S ( R G ) and of the quotient group S ( R G ) / G p are given when R is perfect and G is arbitrary whose G / G p is p -divisible....

Basic subgroups in commutative modular group rings

Peter Vassilev Danchev (2004)

Mathematica Bohemica

Let S ( R G ) be a normed Sylow p -subgroup in a group ring R G of an abelian group G with p -component G p and a p -basic subgroup B over a commutative unitary ring R with prime characteristic p . The first central result is that 1 + I ( R G ; B p ) + I ( R ( p i ) G ; G ) is basic in S ( R G ) and B [ 1 + I ( R G ; B p ) + I ( R ( p i ) G ; G ) ] is p -basic in V ( R G ) , and [ 1 + I ( R G ; B p ) + I ( R ( p i ) G ; G ) ] G p / G p is basic in S ( R G ) / G p and [ 1 + I ( R G ; B p ) + I ( R ( p i ) G ; G ) ] G / G is p -basic in V ( R G ) / G , provided in both cases G / G p is p -divisible and R is such that its maximal perfect subring R p i has no nilpotents whenever i is natural. The second major result is that B ( 1 + I ( R G ; B p ) ) is p -basic in V ( R G ) and ( 1 + I ( R G ; B p ) ) G / G is p -basic in V ( R G ) / G ,...

Basic subgroups in modular abelian group algebras

Peter Vassilev Danchev (2007)

Czechoslovak Mathematical Journal

Suppose F is a perfect field of c h a r F = p 0 and G is an arbitrary abelian multiplicative group with a p -basic subgroup B and p -component G p . Let F G be the group algebra with normed group of all units V ( F G ) and its Sylow p -subgroup S ( F G ) , and let I p ( F G ; B ) be the nilradical of the relative augmentation ideal I ( F G ; B ) of F G with respect to B . The main results that motivate this article are that 1 + I p ( F G ; B ) is basic in S ( F G ) , and B ( 1 + I p ( F G ; B ) ) is p -basic in V ( F G ) provided G is p -mixed. These achievements extend in some way a result of N. Nachev (1996) in Houston...

Certain additive decompositions in a noncommutative ring

Huanyin Chen, Marjan Sheibani, Rahman Bahmani (2022)

Czechoslovak Mathematical Journal

We determine when an element in a noncommutative ring is the sum of an idempotent and a radical element that commute. We prove that a 2 × 2 matrix A over a projective-free ring R is strongly J -clean if and only if A J ( M 2 ( R ) ) , or I 2 - A J ( M 2 ( R ) ) , or A is similar to 0 λ 1 μ , where λ J ( R ) , μ 1 + J ( R ) , and the equation x 2 - x μ - λ = 0 has a root in J ( R ) and a root in 1 + J ( R ) . We further prove that f ( x ) R [ [ x ] ] is strongly J -clean if f ( 0 ) R be optimally J -clean.

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