摘要:

The object of this paper is the calculation of the simple direct summands of the group algebra Q[G] when G = SL(2,q). We assume the character table of G is available and make the computation from that information. There is a well known procedure for finding the number of simple components. For each irreducible complex character γ, one forms the sum γ + γτ+ … of all the algebraic conjugates of γ. The sums obtained this way correspond one-to-one with the simple components. The dimension over Q of a simple component is determined from the characters corresponding to it. Furthermore, it is a full matrix ring over a division ring. Aside from the information obtained from the character table, then, all that is needed is a knowledge of the division rings that occur. The main result of the paper identifies the division rings in the simple component corresponding to the irreducible characters of G.

ISSN:0092-7872    

DOI:10.1080/00927877408548606

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

This paper continues the study of codivisible modules, whose definition is a “dualization” of Lambek's concept [4] of a divisible module relative to a torsion theory. The main purpose of this work is to give a solution to the following problem posed by Bland [2]: “It would be interesting to know under what conditions the universal existence of codivisible covers implies that of projective covers.” The if-and-only-if nature of the solution, which is given in Theorems 2 and 4, shows that our sufficient conditions are “best possible” conditions. The method of the solution introduces the concept of a pseudo-hereditary torsion theory, which may be of interest in its own right; in particular, every hereditary torsion theory and every faithful torsion theory is pseudo-hereditary. The main results for a pseudo-hereditary torsion theory (T, F) relate the conditions, R/T(R) is semiperfect and R/T(R) is left perfect, to the existence of codivisible covers (see Theorems 1 and 3 and Corollaries 1 and 2).

ISSN:0092-7872    

DOI:10.1080/00927877408548607

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

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 Kn(R) = Kn(R{X}), where Knrefers to the Quillen K-theory. The result can be stated in the equivalent form that Hn(G1(R),Z) = Hn(G1(R{X}),Z). From this result it follows that if F is a free ring without unit, then Kn(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 Kn(R) → Knk-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).

ISSN:0092-7872    

DOI:10.1080/00927877408548608

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

In this paper we prove that every coseparable involutory Hopf algebra over the ring of integers Z which is a free Z-module is the group ring of some group. This result was proved independently for Hopf algebras which are finitely generated Z-modules by H.-J. Schneider [6], using similar techniques. We then give some examples of coseparable Hopf algebras over number rings which are not group algebras, and give an example of a cocommutative coseparable coalgebra over a number ring which cannot be given a multiplicative structure making it into a Hopf algebra. The Hopf algebra structure theory required for this paper is found in [1], [4], and [5]. For completeness we give proofs here of the coalgebra analogues to some “well-known” facts about separable algebras.

ISSN:0092-7872    

DOI:10.1080/00927877408548609

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Rings are associative and have a unit and subrings are assumed to have the same unit. Ring homomorphisms are unitary, as are modules. Ideal means two-sided ideal.

ISSN:0092-7872    

DOI:10.1080/00927877408548610

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor