Let V {\displaystyle {}V} denote a vector space over K {\displaystyle {}{\mathbb {K} }} , endowed with an inner product ⟨ − , − ⟩ {\displaystyle {}\left\langle -,-\right\rangle } . Let ‖ − ‖ {\displaystyle {}\Vert {-}\Vert } denote the associated norm