For a standard real or complex inner product, $\langle x,x\rangle=\sum_j|x_j|^2\ge0$. The value is always real, even when the coordinates are complex. This positivity is the basis of the induced length.
Like how this is organised?
Build your own knowledge tree on knowen.md: notes, decisions and tasks in one connected markdown graph, shared with your team and your AI agents.