منابع مشابه
Skew Products and Crossed Products by Coactions
Given a labeling c of the edges of a directed graph E by elements of a discrete group G, one can form a skew-product graph E ×c G. We show, using the universal properties of the various constructions involved, that there is a coaction δ of G on C∗(E) such that C∗(E ×c G) is isomorphic to the crossed product C ∗(E) ×δ G. This isomorphism is equivariant for the dual action δ̂ and a natural action ...
متن کاملDouble-crossed chords and distance-hereditary graphs
An early characterization of distance-hereditary graphs is that every cycle of length 5 or more has crossing chords. A new, stronger, property is that in every cycle of length 5 or more, some chord has at least two crossing chords. This new property can be characterized by every block being complete multipartite, and also by the vertex sets of cycles of length 5 or more always inducing 3-connec...
متن کاملCrossed complexes, free crossed resolutions and graph products 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 by a Coalgebra
We introduce the notion of a crossed product of an algebra by a coalgebra C, which generalises the notion of a crossed product by a bialgebra well-studied in the theory of Hopf algebras. The result of such a crossed product is an algebra which is also a right C-comodule. We find the necessary and sufficient conditions for two coalgebra crossed products be equivalent. We show that the two-dimens...
متن کاملFull Crossed Products by Coactions,
Let δ be a coaction of a locally compact group G on a C*-algebra A. We show that if I is a δ-invariant ideal in A, then 0! I¬δ I G!A¬δ G! (A}I )¬δI G! 0 for full crossed products, as Landstad et al. have done for spatial crossed products by coactions. We prove that for suitable coactions, the crossed products of C ! (X )-algebras are again C ! (X )-algebras, and the crossed products of continuo...
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ژورنال
عنوان ژورنال: Nagoya Mathematical Journal
سال: 1963
ISSN: 0027-7630,2152-6842
DOI: 10.1017/s0027763000011211