[FOM] Eliminability of AC

[joeshipman@aol.com]

Any arithmetical statement provable in ZFC is provable in ZF; AC is 
also eliminable from proofs of Pi^1_2 statements by Shoenfield 
Absoluteness. What is the simplest example of a well-known open problem 
in "ordinary mathematics" (that is, one of interest to mathematicians 
in general and not primarily of interest to logicians and set 
theorists) where there is a possibility some form of Choice is needed 
for any proof?

-- JS
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