Is belonging not defined in axiomatic set theory?
129334
Where does $\in$ come from and where is it defined?
81509
The cardinality of a countable union of countable sets, without the axiom of choice
97951
Is the void set (∅) a proper subset of every set?
30660
Empty set does not belong to empty set
139992
Is power-associativity finitely axiomatizable?
74734
(Enderton set theory) Hartog's theorem and cardinal numbers
88566
Is denying "Paradoxical Partitioning" equivalent to accepting the Axiom of Choice?
144899
Do We Need the Axiom of Choice for Finite Sets?
3663
Finding counterexamples in elementary set theory.
9330
Meaning behind Filter in Set Theory
3072
If the empty set is a subset of every set, why isn't $\{\emptyset,\{a\}\}=\{\{a\}\}$?
31509
Is axiom of choice necessary for proving that every infinite set has a countably infinite subset?
25834
Proof a set cannot contain its own powerset - Russell's Paradox
115675
Strange consequences of Axiom of Choice in Zermelo set theory
53025
Why the need of Axiom of Countable Choice?
16796
Zermelo-Fraenkel set theory and Hilbert's axioms for geometry
4383
Finitely generated monoids - how to show that there is not first order set axiomatizing them.