49

Answers
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7
How long can it take to generate a $\sigma$-algebra?
8
A Fraïssé class without the strong amalgamation property.
5
dense orders are saturated
1
Self-containing structures
3
Bijective-equivalent collections of proper classes in set theory
1
How long should one wait for a report before asking about its status?
14
Similarities between Post’s Problem and Cohen’s Forcing
12
Topological characterization of the closed interval $[0,1]$.
2
Are all models of ZF + DC + “All set of reals are lebesgue measurable” also models of CH?
11
Kunen’s inconsistency result
2
Notation for upperbound power sets.
19
What axioms are used to prove Godel’s Incompleteness Theorems?
7
Connectedness of the complement of small subsets (extended question)
11
What axioms are stronger than the Axiom of choice?
6
Does ZFC prove the universe is linearly orderable?
4
Statement of consistency in Godel’s second incompleteness theorem
11
Are there any natural recursively but not primitive-recursively axiomatized theories?
12
Forcing over set theory versus forcing over arithmetic
6
Z_2 versus second-order PA
9
Can we find strong fixed-points in the fixed-point lemma of Gödel’s incompleteness theorem, that is, where the fixed point is syntactically identical to its substitution instance rather than merely provably equivalent to it?
5
ordered fields with the bounded value property, without choice
6
Categoricity in second order logic
7
What is the spectrum of possible cofinality types for cuts in an ordered field? Or in a model of the hyperreals? Or in a nonstandard model of arithmetic?
4
Is there a relational countable ultra-homogeneous structure whose countable substructures do not have the amalgamation property?
5
How elementary can we go?
6
ordered fields with the bounded value property
6
Height of ordered set
10
Are there examples of statements that have been proven whose consistency proofs came before their proofs?
2
Can the twin prime problem be solved with a single use of a halting oracle?
4
What are the most elegant proofs that you have learned from MO?
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