Equivariant Crossed Modules and Cohomology of Groups with Operators

In this paper we study equivariant crossed modules in its link with strict graded categorical groups. The resulting Schreier theory for equivariant group extensions of the type of an equivariant crossed module generalizes both the theory of group extensions of the type of a crossed module and the one of equivariant group extensions.Comment: 20 pag

Cohomological Classification of Ann-categories

The notion of Ann-categories is a categorification of the ring structure. Regular Ann-categories were classified by Shukla algebraic cohomology. In this article, we state and prove the precise theorem on classification for the general case due to Mac Lane cohomology for rings. And an application for classification problem of ring extensions is also introduced.Comment: Comment: 22 pages, this paper covers the paper "Structure of Ann-categories" (arXiv:0805.1505v4 [math.CT] 20 Apr 2009) Comment: Added appendix, removed section 4 Comment: To appear in Mathematical Communication