I have the following theorem
Any infinite set can be written as the countably infinite union of pairwise disjoint infinite subsets
I have found a couple of proofs for this but I was wondering if there is some proof that doesn't use the axiom of choice (and it's equivalent statements). Does there exist such a proof?
No. An amorphous set is infinite but cannot be written even as the union of two disjoint infinite sets, and it is consistent with $\mathsf{ZF}$ without choice that amorphous sets exist.