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Asaf Karagila's user avatar
Asaf Karagila's user avatar
Asaf Karagila's user avatar
Asaf Karagila
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  • Member for 14 years, 5 months
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Does Well-Ordered Interval Power Set "WOIPS" principle , prove $\sf AC$ in $\sf ZFA$?
@GuozhenShen: An old theorem of Truss says that if there is some $\alpha$ such that there are no chains of type $\alpha$ (of distinct cardinals) between $X$ and $\mathcal P(X)$, then the axiom of choice holds.
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Which $L$-like principles are known to be relatively consistent with large cardinals?
I think that pretty much anything (reasonable) can be made compatible with $V=\rm HOD$ and $\sf GCH$.
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Does Well-Ordered Interval Power Set "WOIPS" principle , prove $\sf AC$ in $\sf ZFA$?
Now that the question had been changed entirely, it's an interesting question. I'd suggest to change the name from $\sf GCH^{WO}$ to something else. This is no longer a generalised continuum hypothesis in any sense of the word. Perhaps "Linear Interval Power Set", or $\sf LIPS$.
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Does Well-Ordered Interval Power Set "WOIPS" principle , prove $\sf AC$ in $\sf ZFA$?
@AndrésE.Caicedo is correct. The atoms have no bearing on Specker's proof. If you suspect that it doesn't, simply go through it and edit your question to point out where exactly the assumption that we work in $\sf ZF$ comes into the proof.
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Turning linear ordering into well-ordering
Oh, that's an interesting question. I don't know.
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The equivalence of Dedekind-infinite and dually Dedekind-infinite as a weak form of (AC)
Sure. Look at the set of injective finite sequences, then look at the map which trims the last element from the sequence. It's in a few answers around the site, I'm certain, and you can play with the proof even more to get other crazy ideas.
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Weak extender models for supercompactness without choice
Supercompactness without choice cannot, and should not, be defined via ultrafilters. If Łoś theorem fails, which it bounds to with AC failing this hard, then ultrafilters, and certainly ultrafilters over ordinals, are practically meaningless. What you want to talk about is embeddings.
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Can there be a set larger than any well-founded set?
Oh, I see what you're asking for now. Sure, that can also work. But I was aiming for correct, not optimal.
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Can there be a set larger than any well-founded set?
If we started with $A$ strictly larger, how would that come to be?
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Can there be a set larger than any well-founded set?
It's not well founded... I don't understand your question.
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Long chains of Dedekind finite sets
@YnirPaz: The point is that $\alpha\mapsto A_\alpha$ is an amenable class function, and we can add a predicate for $\{A_\alpha\mid\alpha\in\rm Ord\}$. And moreover, the union of these sets is itself Dedekind-finite.
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Long chains of Dedekind finite sets
Ducking auto portrait.
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Long chains of Dedekind finite sets
Apologies for the bad citation formatting, I'm typing this on my phone.
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Building the real from Dedekind finite sets
To add to what @Wojowu said, this happens in the Cohen model.
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