Collection Of Open Nonempty Sets.
128987
A collection of pairwise disjoint open intervals must be countable
104550
Countable union of countable sets(ZF)
65308
Axiom of Choice: Family of non-empty sets mutually disjoint or not?
33117
Cyclic containment of sets
13779
Canonical copies of sets
70048
In which topologies do open sets maintain open under countable or arbitrary intersection?
107160
Open Set and Measure Theory
80860
How to call a space in which every G$_\kappa$-set is open
106455
intersection of infinite collection of finite sets?
1627
Cartesian product of an arbitrary number of sets
3663
Finding counterexamples in elementary set theory.
142840
Open axioms of equality
137460
How should I think of an open vs. closed set?
129227
An example of neither open nor closed set
72440
Partition a set into $k$ non-empty subsets
92526
Collection of clopen sets form a base for a countable completely regular space
135454
An open interval is an open set?