The structure of corings with a grouplike element

Abstract

Characteristic properties of corings with a grouplike element are analysed. Associated differential graded rings are studied. A correspondence between categories of comodules and flat connections is established. A generalisation of the Cuntz-Quillen theorem relating existence of connections in a module to projectivity of this module is proven.

14 pages, LaTeX, uses diagrams.tex Version to appear in Banach Center Publications