Resumen de Centers: their integrability and relations with the divergence
This is a brief survey on the centers of the analytic differential systems in R 2 . First we consider the kind of integrability of the different types of centers, and after we analyze the focus–center problem, i.e. how to distinguish a center from a focus. This is a difficult problem which is not completely solved. We shall present some recent results using the divergence of the differential system.
