The Friedrichs angle and alternating projections in Hilbert $C^{\ast }$-modules

Bram Mesland, Adam Rennie

Let $B$ be a $C^{\ast }$-algebra, $X$ a Hilbert $C^{\ast }$-module over $B$ and $M,N\subset X$ a pair of complemented submodules. We prove the $C^{\ast }$-module version of von Neumann's alter…