|Shanghai Normal University
Halmos two projections theorem for Hilbert space operators is one of the fundamental results in operator theory. In this talk we will focus on its generalization to the Hilbert C*-module case, and its application in clarifying the Friedrichs angle between two closed submodules. Based on some new characterizations of the closed submodules and their associated projections, we will introduce a new term of separated idempotents. Some properties of the seperated idempotents will be presented.