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Many people find ACC more intuitive than AC ("Pick something from the first set, then something from the second set, then...) and it also doesn't lead to "controversial consequences" (See for eg: Peculiar examples with Axiom of Countable Choice ?)

My question is:
What are the consequences for Set Theory if we replace AC by ACC -as in ZF and ACC assumed true but cannot assume AC ?

Specifically:
1) Are all ZFC ordinals - $\aleph_1$, $\aleph_\omega$, aleph and beth fixed points etc - still well-defined ?
2) Is the Continuum Hypothesis still undecidable ?
3) Are there any striking changes to Large Cardinal properties ? (For eg: "The smallest measurable cardinal can be equal to the smallest strongly inaccessible cardinal")

PS: If the question is too broad, I'd be very happy to be referred to a book/paper.

Edited: Realized from a comment below that ZF + ACC + Not AC was the system I had in mind, otherwise question 2 becomes trivial.

Cosmonut
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    I thought it was automatic that, if you weaken an axiomatic theory, then anything that was undecidable before is still undecidable? – bof Nov 10 '15 at 01:43
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    Following on what bof said in his first comment: https://en.wikipedia.org/wiki/Hartogs_number – Todd Trimble Nov 10 '15 at 01:46
  • Very interesting. I am editing my question accordingly. – Cosmonut Nov 10 '15 at 01:56
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    Surely, if CH could be proved or disproved with ACC, then it could be proved or disproved in set theory with the full AC? So why is 2) a question? – bof Nov 10 '15 at 02:10
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    None of the usual basic theory of alephs uses choice, only the assertion that every cardinal is an aleph. – Eric Wofsey Nov 10 '15 at 02:13
  • Bof: My question is the other way around. I am replacing AC by ACC. So, not clear to me if you can even construct a model of ZF + ACC where CH holds. Also, not sure if forcing requires full AC. – Cosmonut Nov 10 '15 at 02:14
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  • Yes. 2) Yes. 3) Yes. How could $\mathsf{CH}$ not be undecidable, by the way, if it is undecidable in the stronger theory $\mathsf{ZFC}$? Any standard reference should address this. For instance, Jech's set theory book.
  • – Andrés E. Caicedo Nov 10 '15 at 02:26
  • Any model of ZF + AC + CH is also a model of ZF + ACC + CH. Likewise, any model of ZF + AC + not-CH is also a model of ZF + ACC + not-CH. – bof Nov 10 '15 at 02:27
  • @AndrésCaicedo How are limit beth cardinals defined in ZF? How is "strongly inaccessible defined"? If strongly inaccessible cardinals exist, is there necessarily a smallest one? – bof Nov 10 '15 at 02:32
  • @bof Well, for any set $X$ and any ordinal $\alpha$ I can define $\beth_\alpha(X)$ in the usual way; the key axiom is replacement, not choice. As for strong inaccessiblity, that's usually understood to be a property of well-orderable cardinals, i.e. $\aleph$s, so the usual definition works the same way. – Noah Schweber Nov 10 '15 at 02:36
  • @bof Ah, didn't even notice the beths there. Sure, limit beths are not well defined. There are several ways of defining inaccessibility that are now not equivalent, there are recent papers addressing this. (But this is not a problem.) And no, of course you lose the existence of minimal witnesses. – Andrés E. Caicedo Nov 10 '15 at 02:37
  • @AndrésCaicedo Why are limit beths not defined? If I give you a set $X$ and an arbitrary ordinal $\alpha$, I can define the iterated powerset $P_\alpha(X)$, and then let $\beth_\alpha(X)$ be the (probably not well-orderable but oh well) cardinality of this powerset. Am I missing something? – Noah Schweber Nov 10 '15 at 02:39
  • @NoahSchweber In defining what it means for a well-orderable regular limit cardinal $\aleph_\alpha$ to be strongly inaccessible, do you require $\kappa\lt\aleph_\alpha\implies2^\kappa\lt\aleph_\alpha$ or merely $\kappa\lt\aleph_\alpha\implies2^\kappa\not\ge\aleph_\alpha$? – bof Nov 10 '15 at 02:42
  • @NoahSchweber Yes, sure, we can do that. – Andrés E. Caicedo Nov 10 '15 at 02:43
  • @bof That's a good point, I spoke too soon. – Noah Schweber Nov 10 '15 at 02:43
  • @Cosmonut Maybe you want to focus on models of ZF+ACC+$\neg$AC, to make things less trivial? Note, though, that this doesn't really impact anything "low down" like CH: we can have the first failure of choice happen way high up in the cumulative hierarchy. – Noah Schweber Nov 10 '15 at 02:44
  • Actually, there is an old paper by Keisler and Morley where they provide a definition of beth cardinals as well-ordered cardinalities that allows them to prove the Erdős–Rado theorem in $\mathsf{ZF}$. Of course, their beths are not the sizes of iterated power sets. We could go with this definition, why not? – Andrés E. Caicedo Nov 10 '15 at 02:47
  • @Cosmonut Re: large cardinals, if you don't already know about this: assuming AD, $\omega_1$ is measurable! (So is $\omega_2$ - this is harder to prove. See http://mathoverflow.net/questions/33468/measurable-cardinals-under-axiom-of-determinacy) So . . . that's weird! – Noah Schweber Nov 10 '15 at 02:48
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    @Cosmonut Question 2 is still trivial, since we can have only "high-rank" failures of choice. – Noah Schweber Nov 10 '15 at 02:51
  • That's truly incredible ! Thanks for the edit suggestion, BTW. Realized that ZF + "Can assume ACC but not AC" was really what I had in mind - so was getting puzzled by the downvotes. – Cosmonut Nov 10 '15 at 02:52
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    What you describe is not $\sf AC_\omega$. It's $\sf DC$, which is strictly stronger. – Asaf Karagila Nov 10 '15 at 04:25