Can we write the empty set as a union of open intervals?
62542
Why is the empty set considered an interval?
73130
A simple question about open set
82628
Cardinality of a set of closed intervals
137460
How should I think of an open vs. closed set?
148507
Why an open set in $R^n$ might not be written as countable union of disjoint open intervals?
125502
Empty set literal?
128987
A collection of pairwise disjoint open intervals must be countable
27025
How do I choose an element from a non-empty set?
36881
Empty intersection and empty union
99562
"Sum" of positive measure set contains an open interval?
37431
bracket of intervals
134999
Writing empty set as union of basis elements for a topology.
15380
Notation for intervals
80156
Formatting the union of sets
58594
Is the empty set a subset of itself?
82315
is an empty set an element of {empty set}
109219
How do the sets $\emptyset\times B,\ A\ \times \emptyset, \ \emptyset \times \emptyset $ look like?