Essential extensions in radical theory for rings

Abstract

AbstractThe essential cover Mk of a class M is defined as the class of all essential extensions of rings belonging to M. M is called essentially closed if Mk = M. Every class M has a unique essential closure, i.e. a smallest essentially closed class containing M.Let M be a hereditary class of (semi)prime rings. Then M is proved to be a (weakly) special class if and only if M is essentially closed. A main result is that Mk is the smallest (weakly) special class containing M. Further it is shown that the upper radical UM determined by M, is hereditary if and only if UM has the intersection property with respect to Mk.