Standard invariants for crossed products inclusions of factors

Standard Invariants for Crossed

Postnikov invariants of crossed complexes

We determine the Postnikov tower and Postnikov invariants of a crossed complex in a purely algebraic way. Using the fact that crossed complexes are homotopy types for filtered spaces, we use the above “algebraically defined” Postnikov tower and Postnikov invariants to obtain from them those of filtered spaces. We argue that a similar “purely algebraic” approach to Postnikov invariants may also ...

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 ...

Crossed 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...

Landstad’s characterization for full crossed products

Full C∗-crossed products by actions of locally compact groups are characterized via the existence of suitable maximal coactions, in analogy with Landstad’s characterization of reduced crossed products.