Strong Lifting Splits

Abstract

The concept of an enabling ideal is introduced so that an ideal I is strongly lifting if and only if it is lifting and enabling. These ideals are studied and their properties are described. It is shown that a left duo ring is an exchange ring if and only if every ideal is enabling, that Zhou's delta-ideal is always enabling, and that the right singular ideal is enabling if and only if it is contained in the Jacobson radical. The notion of a weakly enabling left ideal is defined, and it is shown that a ring is an exchange ring if and only if every left ideal is weakly enabling. Two related conditions, interesting in themselves, are investigated: the first gives a new characterization of delta-small left ideals, and the second characterizes weakly enabling left ideals. As an application (which motivated the paper), let M be an I-semiregular left module where I is an enabling ideal. It is shown that m is an element of M is I-semiregular if and only if m - q is an element of IM for some regular element q of M and, as a consequence, that if M is countably generated and IM is delta-small in M, then M congruent to circle plus(infinity)(i=1) Rei where e(i)(2) = ei is an element of R for each i. (C) 2010 Elsevier B.V. All rights reserved.