Countable sums in ZF

[Mikhail Katz]

Hi Tim,

Thanks for mentioning our result.

Just a small correction: we don't literally prove that the result on a
positive function "requires countable choice".

What we show is that it cannot be proved in ZF.

Conceivably weaker forms of AC could be sufficient to establish the
result but we haven't thought about that.

Perhaps folks at FoM could share their insights.

MK