On the Moore-Penrose inverse in C*-algebras

Abstract

In this article, two results regarding the Moore-Penrose inverse in the frame of C*-algebras are considered. In first place, a characterization of the so-calle reverse order law is given, which provides a solution of a problem posed by M. Mbekhta. On the other hand, Moore-Penrose hermitian elements, that is C*-algebra elements which coincide with their Moore-Penrose inverse, are intro- duced and studied. In fact, these elements will be fully characterized both in the Hilbert space and in the C*-algebra setting. Furthermore, it Will be proved that an element is normal and Moore-Penrose hermitian if and only if it is a hermitian partial isometry.