If $A$ is an empty set, how should I understand $\forall x\in A$?
72064
True,  false,  or meaningless?
125502
Empty set literal?
22804
Interpretation of limsup-liminf of sets
97373
Is whether a set is closed or not a local property?
154230
In $\mathsf{ZF}$, for each set $A$ exists an ordinal $\alpha$ such that no surjection $A\to \alpha$ exists
25710
$A ⊂ B$ if and only if $A − B = ∅$
39020
Why is empty set an open set?
88823
How can the empty set be open in the definition of the cofinite topology?
31212
The existence of the empty set is an axiom of ZFC or not?
49385
Proving $\forall x (A\to B) \to(A \to \forall x B):x\notin \mbox{free}(A)$ in a Hilbert system where it is not an axiom
28523
When would the intersection of the empty set mean anything?
155233
$A=\emptyset $ if and only if $B = A \bigtriangleup B$
73130
A simple question about open set
17525
Why the interior of $\mathbb{Q}$ in $\mathbb{R}$ is empty?
33064
Powerset of set with empty sets
131983
Prove that $A \subset B$ if and only if $A \setminus B = \emptyset$
58285
Is it true that if $X$ is connected, then for every nonempty proper subset $A$ of $X$, we have $\mathbf{Bd} \ne \emptyset$