Sum of Closed Subsets of $\mathbb{R}$
28683
Sum of two closed sets in $\mathbb R$ is closed?
148992
A finite set is closed
11405
If a nonempty set of real numbers is open and closed, is it $\mathbb{R}$? Why/Why not?
66239
Verifying that a certain collection of intervals of $\mathbb R$ forms a topology
158569
Proving a particular subset of $R^n$ is closed
143105
Show that, for every real number a, the set {$x ∈ S | f(x) ≤ a$} is a closed subset of $\mathbb R^d$
141762
The direct sum of two closed subspace is closed? (Hilbert space)
33040
Using Zorn's lemma show that $\mathbb R^+$ is the disjoint union of two sets closed under addition.
78117
Closed property of nonempty finite set
149820
How do you prove the set $G = \{(x, f(x)) \mid x \in \mathbb R\}$ is closed?
124562
$f:\mathbb{R}^n \to \mathbb{R}$ has expansion $\sum_i g_i(x)x^i$
74498
Smallest dense subset of $\mathbb{R}$
119606
Closed form of summation
63879
Prove that $\sum_{k=0}^r {m \choose k} {n \choose r-k} = {m+n \choose r}$
11817
Proving that every set $A \subset \Bbb N$ of size $n$ contains a subset $B \subset A$ with $n | \sum_{b \in B} b$
139078
Infinite partition of $\mathbb N$ by infinite subsets
44704
familly of Radially open sets in $\mathbb{R}^2$