On dense subrings of RFM(R) (Q1090397)

This paper concerns subrings T of the endomorphism ring of a countable rank free R-module which contain all finite rank endomorphisms, where R is an arbitrary unital ring. The author characterizes those rings R for which there exists such a T having an automorphism which does not preserve finite rank endomorphisms. He also shows that every functor F on rings mapping each R to a unital such T must have a fixed point, i.e. there is a ring R with R isomorphic to F(R).