Comodules and contramodules over coalgebras associated with locally finite categories

Abstract

We explain how to attach a coalgebra $\mathcal C$ over a field $k$ to a small $k$-linear category $\mathsf E$ satisfying suitable finiteness conditions. In this context, we study full-and-faithfulness of the contramodule forgetful functor, and describe explicitly the categories of locally finite left $\mathcal C$-comodules and left $\mathcal C$-contramodules as certain full subcategories of the category of left $\mathsf E$-modules.