The diagonal in $T_1$ space.
102485
Showing that a topological space is ${\rm T}_1$
6681
How does Cantor's diagonal argument work?
127304
Understanding the algebra of polynomials on a linear space
47653
Cantor diagonalization and fundamental theorem
12293
Let X be a T1 space, and show that X is normal if and only if each neighbourhood of a closed set F contains the closure of some neighbourhood of F
141794
Invariant subspaces of specific dimension
52014
Showing $(C[0,1], d_1)$ is not a complete metric space
2056
A space is $T_{0}$ if and only if the closures of singletons are distinct
120766
Prove ${y_n}$ is a basis for a Hilbert space $H$.
135316
A basic question on diagonalizability of a matrix
127025
Diagonalization of a projection
52928
If $\mathrm{Tr}(A)=0$ then $T=R^{-1}AR$ has all entries on its main diagonal equal to $0$
15596
Identification of each tangent space $T_pV$ with $V$ itself?
62303
For $V$ vector space of dimension $n$ under $\mathbb C$ and $T: V \to V $ linear transformation , show $V= \ker T^n \oplus $ Im $T^n$
72541
Is the matrix diagonalizable for all values of t?
125962
The set $A'$ is closed in a $T_1$ space
59531
Do $T$-invariant subspaces necessarily have a $T$-invariant complement?