Is $(V^\perp)^\perp=\overline{V}$ when $V$ is a subspace of a Hilbert space $H$?
103923
Double orthogonal complement is equal to topological closure
77361
How to prove $|H|[K:K \cap (g^{-1}Hg)]=|K|[H:H \cap (gKg^{-1})]$?
124786
Prove that V contains a subspace of each dimension
118134
If $\psi h$ is in $L^2$ for all $h\in L^2$, must $\psi$ be essentially bounded?
82464
$U^*\otimes V$ versus $L(U,V)$ for infinite dimensional spaces
14550
Every Hilbert space has an orthonomal basis - using Zorn's Lemma
100161
Is it true that $\dim(X) \leq \dim(X^{\ast})$ for every infinite dimentional Banach space $X$?
83360
The completion of a separable inner product space is a separable Hilbert space
12212
Showing a certain subspace of Hilbert space is dense
133609
orthonormal system in a Hilbert space
131998
let ${v_1}, {v_2} $ be orthonormal basis for subspace $W$. Prove that if $z$ is a vector in $W$, then
15300
How to show that $(W^\bot)^\bot=W$ (in a finite dimensional vector space)
95481
The set of self-adjoint operators over a Hilbert space doesn't form a lattice
15793
Is the formula $(\text{ker }A)^\perp=\text{im }A^T$ necessarily true?
154270
Why is $ \overline{e^z} = e^\overline{z} $?
16692
a representation condition of Hilbert space
22297
Normal operator $\Rightarrow$ S invariant implies $S^\perp$ invariant