Is there a countable transitive model satisfying the same set of first-order sentences as $V$?
135524
Is $\mathrm{ZFC}^E$ outright inconsistent?
38711
When can uncountable nouns be countable?
67451
Building a bijection from a finite union of countable sets to $\mathbb{N}$
118595
Proving that a set is countable by finding a bijection
42835
Example of a relation that is symmetric and transitive, but not reflexive
4383
Finitely generated monoids - how to show that there is not first order set axiomatizing them.
106670
Existence of vector space complement and axiom of choice
114550
Well-ordering theorem and second-order logic
153652
Countable ordinals are embeddable in the rationals $\Bbb Q$ -- proofs and their use of AC
98518
Cardinality of equivalence relations on N
136883
The class of equivalence.
34298
sequentially continuous on a non first-countable
127596
Composition of equivalence relations
78225
Countable additivity implies countable subadditivity?
24685
Expressing a Countable Union of Sets as the Countable Union of Disjoint Sets (e.g. Eliminating Duplicate Intersections)
122506
Relation on countable sets
104550
Countable union of countable sets(ZF)