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I've recently started learning Category theory- and I have a pondering- wondering if anyone can help.

Is it possible for two categories to satisfy two different set-axiom system. Namely- is it possible for two distinct categories $SetZFC$ and $SetZF\neg C$ to exists? One satisfying AC and the other negating it?

And finally, and more generally- Are categories subjected to any a-priory set of set-axioms? or are those axioms given as information in a given category?


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up vote 3 down vote accepted

The question seems to me can you describe the difference in the language of categories? In $Set(ZFC)$ every epimorphism splits, in $Set(ZF\neg C)$ not.

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I think your second is supposed to be $Set(ZF\neg C)$... –  Arturo Magidin Mar 23 '11 at 22:38
Thanks, indeed. –  scineram Mar 24 '11 at 12:00
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Yes, this is modelable in topos theory. The axiom of choice for toposes says that the any infinite product of non-initial objects is non-initial (one way to state it) or that every epi splits (as noted above). Look up Bill Lawvere's ETCS, which has a choicified version and an non-choicified version.

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