Intereting Posts

What is the 'implicit function theorem'?
Why is the determinant equal to the index?
Can $\mathbb CP^n$ be the boundary of a compact manifold?
Evaluate Integral with $e^{ut}\ \Gamma (u)^{2}$
$5^n+n$ is never prime?
Generalized Cross Product
A question about $\prod_{x\in \mathbb{R}^{*}}{x}$
One more question about decay of Fourier coefficients
Find points along a Bézier curve that are equal distance from one another
If an IVP does not enjoy uniqueness, then there are infinitely many solutions.
Smallest example of a group that is not isomorphic to a cyclic group, a direct product of cyclic groups or a semi direct product of cyclic groups.
Non-Circular Proof of $\lim_{x \to 0} \frac{\sin x}{x} = 1$
Given $A$ and $B$ positive-definite matrices and $Q$ unitary matrix, prove that if $A = BQ$, then $A=B$.
Jordan normal form and invertible matrix of generalized eigenvectors proof
Ideal in $\mathbb Z$ which is not two-generated

Let $E$ be a $T_1$ space, and $A\subset E$ , I need to prove that $A’$ is closed, so my idea is to prove that $C_{E}A’$ is open i.e a neighborhood of all it’s point.

But how to do this ?

- What is the relation between $ \kappa$-monolithic and monotonically monolithic?
- Proving the closed unit ball of a Hilbert space is weakly sequentially compact
- What does continuity of inclusion means?
- $\forall A\subset \mathbb{N}$ the sum of the reciprocals of $A$ diverges iff $A$ is $(\tau, \mathbb{N})$-dense
- Prove that the countable complement topology is not meta compact?
- Picturing the discrete metric?

- an homeomorphism from the plane to the disc
- If $S\times\mathbb{R}$ is homeomorphic to $T\times\mathbb{R}$, and $S$ and $T$ are compact, can we conclude that $S$ and $T$ are homeomorphic?
- How to prove boundary of a subset is closed in $X$?
- 1-1 correspondence between and
- Is “connected, simply connected” Redundant?
- every non-principal ultrafilter contains a cofinite filter.
- Idempotence of the interior of the closure
- Closed image of locally compact space
- What does Structure-Preserving mean?
- Theorem of Arzelà-Ascoli

HINT: If $x\in E\setminus A’$, then $x$ has an open nbhd $U_x$ such that $U_x\cap A$ contains at most one point. Show that $U_x\cap A’=\varnothing$.

- Expected Value with stopping rule.
- What is the importance of the Poincaré conjecture?
- Probability to find the sequence “Rar!” in a random (uniform) bytes stream at a position $\le n$
- How to prove that derivatives have the Intermediate Value Property
- What is the order of $(\mathbb{Z} \oplus \mathbb{Z})/ \langle (2,2) \rangle$ and is it cyclic?
- Identify $P(2014)$ if $P(i)=1/i$ for every positive integer $1\le i\le2013$
- What's an easy way of proving a subgroup is normal?
- Are there any continuous functions from the real line onto the complex plane?
- Why doesn't $d(x_n,x_{n+1})\rightarrow 0$ as $n\rightarrow\infty$ imply ${x_n}$ is Cauchy?
- To find area of the curves that are extension of ellipse
- Does there exist a non-empty set that is a subset of its power set?
- How many different sets of $6$ different numbers can we construct from $11, 13, 18, 19, 19, 20, 23, 25$?
- Generating a Eulerian circuit of a complete graph with constant memory
- Prove $f(S \cup T) = f(S) \cup f(T)$
- A generalization of a divisibility relation for Fibonacci numbers