New posts in Hilbert Spaces

$P+Q-PQ$ is a projection if and only if $PQ=QP$.

What really is ''orthogonality''?

Two operators $X$ and $Z$ in an infinite dimensional Hilbert space satisfying $X^2=Z^2=I$ and $\{X,Z\}= 0$

Vector space that can be made into a Banach space but not a Hilbert space

Polar decomposition of Bounded Normal Operator on Hilbert Space

Is every Banach space densely embedded in a Hilbert space?

Compatible Hilbert space subspaces - need help understanding a statement made in a book

Countably Infinitely Many Points in a Euclidean Space with Restraining Orders

Show $ \langle Tx,x \rangle \in \Bbb R\ \forall x \in H\ \implies T$ is self-adjoint

Prob. 8, Sec. 3.5 in Erwin Kreyszig's Introductory Functoinal Anlaysis With Applications