Skip to main content
Asaf Karagila's user avatar
Asaf Karagila's user avatar
Asaf Karagila's user avatar
Asaf Karagila
Moderator
  • Member for 14 years, 5 months
  • Last seen this week
Loading…
comment
How many algebraic closures can a field have?
@DavidRoberts: Should, yes. One day...
comment
What topos-theoretic construction lies behind the “symmetric model” construction (used to refute AC) in Set Theory?
Just another anecdote on name changes, Uri Abraham was (and in Hebrew, still is) Uri Avraham. He said that while he was a postdoc in the US, people confused those two names enough for him to give up and change.
comment
Can this semi-constructible structure satisfy existence of a measurable cardinal?
My point is that you seem to be asking about some kind of a constructible concept compatible with measurable cardinals, and that already exists. Jech has an introduction to it, as will Kanamori, and at least two chapters in the Handbook of Set Theory come to mind.
comment
Can this semi-constructible structure satisfy existence of a measurable cardinal?
Are you asking if measurable cardinal are compatible with the universe being constructible from a set? Yes, they are. $L[D]$, when $D$ is a measure on $\kappa$, is such an example. It is not at all clear what these axioms actually mean, though. Or are you just asking if we can create some kind of a filtration of the universe whose successor steps don't increase in cardinality for infinite indices? In which case, also yes.
awarded
comment
Can there be a proper class of Dedekind-finite cardinals?
@GuozhenShen: The @ notifications only work if you actually type in the user name, not the last name. That doesn't do anything.
comment
Can there be a proper class of Dedekind-finite cardinals?
@Elliot: If you can do it once, you can do it forever. That's kind of the point in my paper.
awarded
awarded
Loading…
comment
Topologically symmetric models of $\mathsf{ZFA}$
@Joel: That is unfortunate, but ZFA is fairly the standard in the literature on permutation models.
comment
Is "$2^{|X|} = \aleph_{|X|^+}$ for all infinite sets $X$" consistent with ZFC?
@David: The use of $\alpha^+$ as the successor ordinal in some texts which present only the very basic introduction to set theory is somehow understandable (since $x\cup\{x\}$ is, in a good sense, a successor of $x$ as a set). But the notation is unambiguously used in set theory to mean the cardinal successor. Indeed, one of the few cases of notation meaning "pretty much just the one thing" that I can think of in set theory.
awarded
revised
Loading…
comment
comment
What is the consistency strength of "Singular worldly that is inaccessible in an inner model"?
Ahh, okay. I see what you mean now. Yes, I had meant sharps stronger than $0^\#$, but it seems that's not going to be the case necessarily.
comment
What is the consistency strength of "Singular worldly that is inaccessible in an inner model"?
Even more confused now... $V_\eta^{L[0^\#]}\models V=L[0^\#]$... Right? And so it is a model of $\sf ZFC$ in which there are no worldly cardinals.