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# Questions

5
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### Can there be an almost-special not-fully-special Aronszajn tree?

mar 26 12 at 7:36 Joel David Hamkins 75.4k8188346

10
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262
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### Can a model of set theory be realized as a Cohen-subset forcing extension in two different ways, with different grounds and different cardinals?

feb 1 at 20:57 Joel David Hamkins 75.4k8188346

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### What is the computational-complexity-theoretic analogue of computable inseparability? For example, if P is not NP, are there disjoint NP sets with no separation in P?

mar 1 12 at 14:21 Emil Jeřábek 10.7k12441

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598
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### 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?

aug 12 11 at 10:36 Emil Jeřábek 10.7k12441

2
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387
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### Which are the rigid suborders of the real line?

dec 29 09 at 5:23 François G. Dorais 22.7k249114

6
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4
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663
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### Does every decidable question about finitely presented groups amount to a question about abelian groups?

feb 27 10 at 17:33 HW 10.1k12366

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625
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### If Q is a subset of the plane of size less than continuum, then does every closed F in Q extend to a closed connected G in the plane with the same trace on Q? (Or is this independent of ZFC?)

nov 17 10 at 16:10 vm 1

7
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### Can there be a global linear ordering of the universe without a global well-ordering of the universe?

nov 3 at 18:07 Joel David Hamkins 75.4k8188346