some important proofs about adjoint operators
109792
Divergence as transpose of gradient?
136909
Functional Analysis: The rank of an operator detemines if it's a compact operator.
55067
Norm of self-adjoint operator
28719
Question about Angle-Preserving Operators
55488
Proving that $\operatorname{codim}(X,Y)=\dim(\mathcal{O}_{X,\eta})$
55388
Finding nilpotent and diagonalizable operators for a linear transformation $T$
144221
Matrix determinant lemma with adjugate matrix
26570
Prove $\operatorname{rank}(AB) = \operatorname{rank}(B)$
156877
Rank-one perturbation proof
60514
Isometric  Left Inverse Adjoint
141015
Proof of orthogonal matrix
52198
Why is every selfadjoint operator closed?
118049
Show that $\mathbb{R}^{\mathbb{R}} = U_{e} \oplus U_{o}$
137890
Diagonalizable Operators and characteristic polynomials
45071
Having the derivative be an operator
133609
orthonormal system in a Hilbert space
11558
How to show that the limit of compact operators in the operator norm topology is compact