What's the least class of ordinals closed under successor and the limits of omega-sequences?
63618
Can all ordinals be obtained by taking successors and countable limits?
83185
How to show countability of $\omega^\omega$ or $\epsilon_0$ in ZF?
116811
Proofs with limit superior and limit inferior: $\liminf a_n \leq \limsup a_n$
78117
Closed property of nonempty finite set
121860
Number of well-ordering relations on a well-orderable infinite set $A$?
122048
why is the set of all binary sequences not countable?
45878
Elementary Set Theory: Ordinals, Well Orderings and Isomorphisms
68994
Countable closed sets
132298
How do you find the smallest of homeomorphic ordinals?
153652
Countable ordinals are embeddable in the rationals $\Bbb Q$ -- proofs and their use of AC
60004
Why is $\omega$ the smallest $\infty$?
34723
Proof of a limit for a recursively-defined sequence
102490
Does this recursive sequence have a closed-form?
55978
Prove that for every countable ordinal $\alpha$, $\alpha\times[0,1)$ is order isomoprhic to $[0,1)$
23076
Proof of limit of quotient sequence property
1148
Curious limit of a sequence used to prove Etemadi's SLLN
52429
Explicit countable elementary extension of $\mathbb{N}$