4 ms·
> But inside the model there really isn't a bijection between the sets of naturals and reals No. Inside the model, there is exactly such a surjection. We don't
by ogogmad 4y ago
> But inside the model there really isn't a bijection between the sets of naturals and reals
No. Inside the model, there is exactly such a surjection. We don't care what happens outside of it.
Maybe you already knew this, but to clarify: "Countable" means that there exists a surjection, not necessarily a bijection. For instance, the set {a,b,c} is countable, but there is clearly no bijection Nat -> {a,b,c} as one set is infinite and the other's finite.
> It's not too surprising
On the contrary: It's a ground-breaking result IMO.
- deleted 4y ago[deleted]
- drdec 4y agoAs always, this depends on your definitions, e.g. see https://encyclopediaofmath.org/wiki/Countable_set https://encyclopediaofmath.org/wiki/Countable_set
- fdupress 4y agoBy the definition you link, combined with its subdefinition for uncountable, finite sets are uncountable. That is a pretty big leap from accepted terminology.