Löwenheim-Skolem and proper class models of ZFC.
115597
Almost universal class
7007
If $\alpha$ is a regular cardinal, the union of an elementary chain of $\alpha$-saturated models is also a $\alpha$-saturated model
136094
$G_\delta$ singletons in compact Hausdorff and first countability
13436
Robinson arithmetic and its incompleteness
144211
a second course in abstract algebra
31389
consistency of ZF\{Power Set axiom}
3663
Finding counterexamples in elementary set theory.
29756
Classsifying 1- and 2- dimensional Algebras, up to Isomorphism
3465
Equivalence relations and power sets.
30587
Uncountable well ordered set in $Z^-$ theory.
17978
Isomorphism classes of $\mathbb{Z}[i]$ modules.
145933
Localization commutes with Hom for finitely-generated modules
143138
All models of $\mathsf{ZFC}$ between $V$ and $V[G]$ are generic extensions of $V$
153652
Countable ordinals are embeddable in the rationals $\Bbb Q$ -- proofs and their use of AC
135760
Can proper classes also have cardinality?
154324
preservation of completeness under homeomorphism
85398
$\mathsf{ZF}$ is not finitely axiomatizable