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On Some Fully Invariant Subgroups of Summable Groups

Peter Danchev — 2008

Annales mathématiques Blaise Pascal

We show the inheritance of summable property for certain fully invariant subgroups by the whole group and vice versa. The results are somewhat parallel to these due to Linton (Mich. Math. J., 1975) and Linton-Megibben (Proc. Amer. Math. Soc., 1977). They also generalize recent assertions of ours in (Alg. Colloq., 2009) and (Bull. Allah. Math. Soc., 2008)

Warfield invariants in abelian group rings.

Peter V. Danchev — 2005

Extracta Mathematicae

Let R be a perfect commutative unital ring without zero divisors of (R) = p and let G be a multiplicative abelian group. Then the Warfield p-invariants of the normed unit group V (RG) are computed only in terms of R and G. These cardinal-to-ordinal functions, combined with the Ulm-Kaplansky p-invariants, completely determine the structure of V (RG) whenever G is a Warfield p-mixed group.

Invo-regular unital rings

Peter V. Danchev — 2018

Annales Universitatis Mariae Curie-Skłodowska, sectio A – Mathematica

It was asked by Nicholson (Comm. Algebra, 1999) whether or not unit-regular rings are themselves strongly clean. Although they are clean as proved by Camillo-Khurana (Comm. Algebra, 2001), recently Nielsen and Ster showed in Trans. Amer. Math. Soc., 2018 that there exists a unit-regular ring which is not strongly clean. However, we define here a proper subclass of rings of the class of unit-regular rings, called invo-regular rings, and establish that they are strongly clean. Interestingly, without...

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 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...

G -nilpotent units of commutative group rings

Peter Vassilev Danchev — 2012

Commentationes Mathematicae Universitatis Carolinae

Suppose R is a commutative unital ring and G is an abelian group. We give a general criterion only in terms of R and G when all normalized units in the commutative group ring R G are G -nilpotent. This extends recent results published in [Extracta Math., 2008–2009] and [Ann. Sci. Math. Québec, 2009].

Commutative modular group algebras of p -mixed and p -splitting abelian Σ -groups

Peter Vassilev Danchev — 2002

Commentationes Mathematicae Universitatis Carolinae

Let G be a p -mixed abelian group and R is a commutative perfect integral domain of char R = p > 0 . Then, the first main result is that the group of all normalized invertible elements V ( R G ) is a Σ -group if and only if G is a Σ -group. In particular, the second central result is that if G is a Σ -group, the R -algebras isomorphism R A R G between the group algebras R A and R G for an arbitrary but fixed group A implies A is a p -mixed abelian Σ -group and even more that the high subgroups of A and G are isomorphic, namely, A G . Besides,...

On extensions of primary almost totally projective abelian groups

Peter Vassilev Danchev — 2008

Mathematica Bohemica

Suppose G is a subgroup of the reduced abelian p -group A . The following two dual results are proved: ( * ) If A / G is countable and G is an almost totally projective group, then A is an almost totally projective group. ( * * ) If G is countable and nice in A such that A / G is an almost totally projective group, then A is an almost totally projective group. These results somewhat strengthen theorems due to Wallace (J. Algebra, 1971) and Hill (Comment. Math. Univ. Carol., 1995), respectively.

Isomorphism of commutative group algebras of p -mixed splitting groups over rings of characteristic zero

Peter Vassilev Danchev — 2006

Mathematica Bohemica

Suppose G is a p -mixed splitting abelian group and R is a commutative unitary ring of zero characteristic such that the prime number p satisfies p inv ( R ) zd ( R ) . Then R ( H ) and R ( G ) are canonically isomorphic R -group algebras for any group H precisely when H and G are isomorphic groups. This statement strengthens results due to W. May published in J. Algebra (1976) and to W. Ullery published in Commun. Algebra (1986), Rocky Mt. J. Math. (1992) and Comment. Math. Univ. Carol. (1995).

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 ,...

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