Open subsets of the connected sum $M_1\# M_2$
102323
Nice neighborhoods of each "piece" in a manifold connected sum
55659
Sum of closed and compact set in a TVS
72468
Open and closed balls in $C[a,b]$
107370
An open covering of $\mathbb{Q} \cap [0,1]$ that does not contain any finite subcovering
89264
Connectedness in the Quotient Space
26919
Intersection of Connected Sets
99236
Interior of closure of an open set
61816
Cut points and connected space
132541
Showing ${1\over n}\sum|S_i|=O(\sqrt n)$ for $S_i\subset [n]$, $|S_i\cap S_i|\le 1$ for $i\ne j$
72256
Prove there exists two sub-sets of indices $I,J\subseteq [2n]$ such that $\sum_{i\in I}a_i=\sum_{j\in J}b_j$
92639
Prove that the family of open sets in $\mathbb{R}$ has cardinality equal to $2^{\aleph_0}$
18572
Union of a family of connected pairwise not disjoint subspaces is connected
124036
Open affine neighborhood of points
88301
What are all of the connected subsets of $\mathbb{Q}$?
16654
Unions and Intersections of Open Sets are Open
94825
Open set as a finite union of closed sets
151544
Prove that if $B$ is the set of rationals in $[0,1]$ with a finite subcover, then: $1 \leq \sum_{k=1}^n m^*(I_k)$