Prove $M^{\perp}$ is isometric to $(X/M)^*$ where $X$ is a normed space and $M$ is a closed subspace of $X$
117476
Isometries between dual factor space and annihilator
97949
Existence of a $\mathbb C$-Banach space isometric to a Hilbert Space but whose norm is not induced by an inner product?
124786
Prove that V contains a subspace of each dimension
27517
Isometry in compact metric spaces
150287
Spectral radii and norms of similar elements in a C*-algebra: $\|bab^{-1}\|<1$ if $b=(\sum_{n=0}^\infty (a^*)^n a^n)^{1/2}$
137067
For Banach space there is a compact topological space so that the Banach space is isometrically isomorphic with a closed subspace of $C(X)$.
92291
$U_1, U_2, ..., U_k$ subspaces of linear space $X$ with same dimensions, prove $X=U_1\oplus V=U_2\oplus V=...=U_k\oplus V$
93511
Prove that $C^1([a,b])$ with the $C^1$- norm is a Banach Space
102529
Prove that the set $\left\{ x, Ax, \dots, A^{k-1} x \right\}$ is linearly independent
149664
Norm is sup of inner products (proof).
82474
Isometries of $\mathbb{R}^n$
31686
Every metric space can be isometrically embedded in a Banach space, so that it's a linearly independent set
114524
Proof Verification: the orthogonal complement of the column space is the left nullspace
24585
Proving that $\mathbf{W}$+$\mathbf{W^{\perp}}$=$\mathbb{R^{n}}$
128866
Isomorphism between dual space and bilinear forms
68153
How to show that $L^p$ spaces are nested?
141762
The direct sum of two closed subspace is closed? (Hilbert space)