Criteria for preserving the category cohomology for the inverse image

Abstract

The article investigates the question of under what conditions a functor between small categories preserves cohomology groups when passing to the inverse image. For example, it is known that the left adjoint functor preserves the category cohomology with local coefficients or the category cohomology constructed as derived of the limit functor. We give counterexamples showing that the left adjoint functor may not preserve the Baues-Wirsching, Hochschild-Mitchell, and Thomason cohomology. To solve the arising problems, we propose necessary and sufficient conditions for the invariance of these types of cohomology under the transition to the inverse image of a functor between small categories. Moreover, we generalize these cohomology of small categories and find similar criteria for the obtained generalization.