منابع مشابه
Radical Extensions and Crossed Characters
E. Witt has given a theory of abelian extensions of fields containing sufficiently many roots of unity which consists essentially, as has been remarked before, in applying the theory of characters of finite abelian groups. There exists now a sufficiently developed theory of crossed characters, and it is the object of this note to show that a fairly complete and simple theory of radical extensio...
متن کاملCentral extensions of precrossed and crossed modules
The notion of centrality for crossed modules was introduced by Norrie in her thesis [7], in which she studied the category of crossed modules CM from an algebraic point of view, showing suitable generalizations of group theoretic concepts and results. Subsequently, Norrie’s approach was followed by Carrasco, Cegarra and R.-Grandjeán. In [5] they proved that CM is an algebraic category (i.e. the...
متن کاملRadical Extensions of Rings
Jacobson's generalization [5, Theorem 8] of Wedderburn's theorem [8] states that an algebraic division algebra over a finite field is commutative. These algebras have the property that some power2 of each element lies in the center. Kaplansky observed in [7] that any division ring, or, more generally, any semisimple ring, in which some power of each element lies in the center is commutative. Ka...
متن کاملCrossed Complexes, and Free Crossed Resolutions for Amalgamated Sums and Hnn-extensions of Groups
The category of crossed complexes gives an algebraic model of CW -complexes and cellular maps. Free crossed resolutions of groups contain information on a presentation of the group as well as higher homological information. We relate this to the problem of calculating non-abelian extensions. We show how the strong properties of this category allow for the computation of free crossed resolutions...
متن کاملCrossed Products and Cleft Extensions for Coquasi-hopf Algebras
The notion of crossed product with a coquasi-Hopf algebra H is introduced and studied. The result of such a crossed product is an algebra in the monoidal category of right H-comodules. We give necessary and sufficient conditions for two crossed products to be equivalent. Then, two structure theorems for coquasi Hopf modules are given. First, these are relative Hopf modules over the crossed prod...
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ژورنال
عنوان ژورنال: Bulletin of the American Mathematical Society
سال: 1943
ISSN: 0002-9904
DOI: 10.1090/s0002-9904-1943-08002-0