1. Department of Mathematics and Statistics , The University of Melbourne , VIC, 3010, Australia;2. Philosophical Faculty , University of Ni? , Ni?, 18000, Yugoslavia-Serbia
Abstract:
We study necessary and sufficient conditions for the invertibility of the sum f+g when f and g are idempotents in a unital ring or bounded linear operators in Hilbert or Banach spaces. We describe the relation between the invertibility of f+g and f m g.