局部环上正交群中一类子群的扩群

定出了局部环上正交群中一类子群的扩群,得到了如下结果:设R是局部环,M是R的唯一极大理想,O(2m,R)为R上正交群.对R的任意理想S,G(2m,S)表示子群{A BC D∈O(2m,R)|B∈Sm×m}.如果char(R)≠2,m≥3,G(2m,0)≤X≤G(2m,M),那么存在R的理想S,使得X=G(2m,S).     

The ring of quotients of R(S)

A ring of quotients of the semigroup ring R(S) is discussed where R has a σ-set Σ and S has a σ-set Δ. In particular, we study the cases where (1) R is an integral domain and S is a commutative cancellative semigroup, (2) R is a commutative ring and S is a semilattice and (3) R is a commutative ring and S is a Rees matrix semigroup over a semigroup. Communicated by G. Lallement     

Self Extending Rings

A ring R is an IPQ (isomorphic proper quotient)-ring if R ? R/A for every proper ideal A ? R. If every ideal A ? R satisfies: either R ? A or R ? R/A, then R is called an SE (self extending)-ring. It is shown that with one exception, an abelian group G is the additive group of an IPQ-ring if and only if G is the additive group of an SE-ring. The one exception is the infinite cyclic group Z. The zeroring with additive group Z is an SE-ring, but a ring with infinite cyclic additive group is not an IPQ-ring. Since the structure of the additive groups of IPQ-rings is known, the structure of the additive groups of SE-rings is completely determined.     

The Zero-Divisor Graphs Which Are Uniquely Determined By Neighborhoods

A nonempty simple connected graph G is called a uniquely determined graph, if distinct vertices of G have distinct neighborhoods. We prove that if R is a commutative ring, then Γ(R) is uniquely determined if and only if either R is a Boolean ring or T(R) is a local ring with x² = 0 for any x ∈ Z(R), where T(R) is the total quotient ring of R. We determine all the corresponding rings with characteristic p for any finite complete graph, and in particular, give all the corresponding rings of K_n if n + 1 = p^q for some primes p, q. Finally, we show that a graph G with more than two vertices has a unique corresponding zero-divisor semigroup if G is a zero-divisor graph of some Boolean ring.     

On Lie metabelian group rings

Let G be a finite group without elements of orders two and three and R be a commutative ring with characteristic different from 2. If either the subrings A of R(G), the group ring of G over R, generated by the set {g + g^?1; g ∈ G} or B generated by the set {g ? g^?1; g ∈ G} is Lie metabelian, then G is abelian.     

Untergruppen der GL2, welche durch homogene lineare Kongruenzen definiert sind

We generalize a result of Rankin [1]: Let R be a p — adic valuation ring or one of its factor rings and let G be GL₂(R) or SL₂(R). Then for M∈ M₂(R), G_M:={s∈G| trace MS=O} is a group iff trace M=0 and det M satisfies a simple condition (det M=O in most cases). We give similar conditions for several homogeneous linear equations defining subgroups of G.     

分次可除模

对于Ｇ—分次环Ｒ，我们证明如下结论：（１）若Ｒ是分次正则环，则Ｒ上的任一分次左Ｒ—模都是分次可除模；（２）若Ｒ分次非退化且Ｍ是分次可除左Ｒ—模，则Ｍｅ是可除左Ｒｅ—模；（３）若Ｇ是有序群，Ｍ是可除左Ｒ—模，则Ｍ～和Ｍ～是分次可除左Ｒ—模，其中Ｍ为分次左Ｒ—模Ｎ的子模     

Abelsche Galoiserweiterungen von R[X]

Our main result states that for a commutative ring R and a finite abelian group G the following conditions are equivalent: (a) Gal(R,G)=Gal (R[X],G), i.e. every commutative Galois extension of R[X]with Galois group G is extended from R. (b) The order of G is a non-zero-divisor in R/Nil(R). The proof uses lifting properties of Galois extensions over Hensel pairs and a Milnor-type patching theorem.     

GROUP ACTIONS ON VON NEUMANN REGULAR RINGS

ＧＲＯＵＰＡＣＴＩＯＮＳＯＮＶＯＮＮＥＵＭＡＮＮＲＥＧＵＬＡＲＲＩＮＧＳ￥ＺＨＡＮＧＹＩＮＨＵＯＡｂｓｔｒａｃｔ：ＬｅｔＡｂｅａｒｉｎｇｗｉｔｈｉｎｄｅｎｔｉｔｙ，ＧａｆｉｎｉｔｅｇｒｏｕｐｏｆａｕｔｏｍｏｒｐｈｉｓｍｓｏｆＡ．Ｔｈｅｍａｉｎｒｅｓｕ...     

N-环Von-Neumann正则性

环R称为N-环,如果R的素根N(R)=｛r∈R｜存在自然数n使rⁿ=0}.本文不仅对N-环进行了刻划,而且还研究了N-环的VonNeumann正则性.特别证明了：对于N-环R,如下条件是等价的：(1)R是强正则环;(2)R是正则环;(3)R是左SP-环;(4)R是右SF-环;(5)R是MELT,左p-V-环;(6)R是MERT,右p-V-环.因此推广了文献[4]中几乎所有的重要结果,同时也改进或推广了其它某些有关正则环的有用结果.     

K-Theory of Free Rings

The object of this article is to establish the following result (Corollary 3.9 below): If R is a regular right noetherian ring and R{X} is the free associative algebra on the set X, then K_n(R) = K_n(R{X}), where K_n refers to the Quillen K-theory. The result can be stated in the equivalent form that H_n(G1(R),Z) = H_n(G1(R{X}),Z). From this result it follows that if F is a free ring without unit, then K_n(F) = 0, whence free rings are acyclic models for Quillen K-theory (3.11 below). This result in turn enables us to complete Anderson's work [1] in identifying the Quillen K-theory [11] and the K-theory proposed by Gersten [7] and Swan [18] for all rings. We also establish that the natural transformation K_n(R) → K_n ^k-v(R) between the Quillen theory and the K-theory of Karoubi and Villamayor is an isomorphism if R is a supercoherent (Definition 1.2) and regular (Definition 1.3) ring. From this result we can gain some information about the K-theory of group rings of free products of groups (Theorem 5.1).     

Malcev-Neumann环的主拟Baer性质

设R是环，G是偏序群，σ是从G到R的自同构群的映射。本文研究了Malcev-Neumann环R*((G))是主拟Baer环的条件。证明了如下结果：如果R是约化环并且σ是弱刚性的，则R*((G))是主拟Baer环当且仅当R是主拟Baer环，并且I(R)的任意G可标子集在I(R)中具有广义并．     

Two applications of maschke's theorem

Let R ? G denote a crossed product of the finite group G over the ring R and let V be an R ? G-module. Maschke's theorem states that if 1/∣G∣ ε R and if V is completely reducible as an R-module, then V is also completely reducible as an R ? G -module. In this paper, we obtain two applications of this theorem, both under the assumption that R is semiprime with no ∣G∣ -torsion. The first concerns group actions and here we show that if G acts on R and if I is an essential right ideal of the fixed ring R^G , then IR is essential in Rs. This result, in turn, simplifies a number of proofs already in the literature. The second application here is a short proof of a theorem of Fisher and Montgomery which asserts that the crossed product R ? G is semiprime.     

On additive decompositions of the set of primes

We show that there is no set A {\cal A} of integers, such that¶ (P - 1) \subseteqq A + A \subseteqq P è(P - 1) ({\cal P} - {1}) \subseteqq {\cal A} + {\cal A} \subseteqq {\cal P} \cup ({\cal P} - 1) ,¶ where P {\cal P} denotes the set of primes.     

On strong commutativity preserving mappings

Let R be a ring, and S a non-empty subset of R. Suppose that R admits mappings F and G such that [F(x), G(y)] = [x,y] for all x, y ∈ S. In the present paper, we investigate commutativity of the ring R, when the mapping G is assumed to be a derivation or an endomorphism of R.     

单位上三角矩阵群的注记(Ⅲ)

设k_(ij)(1≤ij≤n)是给定的正整数,分别记G={ (1 k12a12…k1na1n 0 1…k2na2n…… 0 0…1 )|aij∈Z},R={ (0 k12a12…k1na1n……0 0…k2na2n 0 0…1 )|aij∈Z},本文证明:当G成群且G的上、下中心群列重合时,其相伴Lie环L(G)与Lie环R同构,其中R的Lie积定义为[A,B]=AB-BA.即得到了此时L(G)的矩阵表示.     

Functors of the category of abelian sheaves on regular affine scheme

In this short paper, we prove that ifR is a regular local ring of unequal characteristic, then there exists an additive covariant functorG from the category of abelian sheaves on SpecR to the category of abelian groups such that id _R (G(R))>dimG(R). This result shows that the answer to the question 3.8 (ii) in [3] may be negative.     

A note on the units of semigroup rings

In [2] Coleman and Enochs obtained results about the units of the polynomial ring R[x] for rings R satisfying a condi-tion which is, in some sense, a generalization of commutativity. In [3] some of these results were extended to group rings over an ordered group. In this note a class of rings larger than the class considered in [2] is used to extend the results in [2] and 3] to the semigroup ring RG, G an u.p, semigroup.

In the last section we give a necessary and sufficient condi-tion for an element to be a divisor of zero in RG where G is an u.p. semigroup.     

The weak global dimension of commutative coherent rings

Let R be a commutative coherent ring and wD(R) denote the weak global dimension of R.We prove that for an integer n≥2 the following are equivalent:.

(a) wD(R)n;.

(b) FP-idM ?Gn-2 for all (FP-)injectives G and for all modules M;.

(c) fdHom(G,M)n-2 for all (FP-)injectives G and for all modules M;.

(d) fdHom(M,G)n-2 for all flat modules G and for all modules M.     

CLASSICAL QUOTIENT RINGS OF GROUP RINGS

Abstract

Throughout G will denote a free Abelian group and Z(R) the right singular ideal of a ring R. A ring R is a Cl-ring if R is (Goldie) right finite dimensional, R/Z(R) is semiprime, Z(R) is rationally closed, and Z(R) contains no closed uniform right ideals. We prove that R is a Cl-ring if and only if the group ring RG is a C1-ring. If RG has the additional property that bRG is dense whenever b is a right nonzero-divisor, then the complete ring of quotients of RG is a classical ring of quotients.