superfluous epimorphism

Given a ring RR (or some analogue, say a Banach algebra), a submodule KK of an RR-module MM is called superfluous or small in MM, written K<<MK \lt\lt M, if, for every submodule LML\subset M , the equality K+L=MK + L = M implies L=ML = M. An epimorphism f:MNf : M\to N is called superfluous (or coessential) if Kerf<<MKer f \lt\lt M.

Superfluous epimorphisms (submodules) are a notion dual to essential monomorphisms (submodules); their role in the study of projective covers is analogous to the role of essential monomorphisms in the study of injective envelopes.

category: algebra

Created on April 1, 2014 06:51:02 by Zoran Škoda (