Angles and Schauder basis in Hilbert spaces

Bingzhe Hou, Yang Cao, Geng Tian +1

Let $\mathcal{H}$ be a complex separable Hilbert space. We prove that if $\{f_n{\}}_{n=1}^{\infty }$ is a Schauder basis of the Hilbert space $\mathcal{H}$, then the angles between…