5:01 AM
This is probably a naive and vague question. And perhaps I should have search first whether something like this was asked on the main. And perhaps this has intersection with the topic of logic chatroom, too.
Often when reading that something is not provable in ZF (as opposed to ZFC), I read something like this: "This means you cannot give an explicit construction of a non-measurable set." "You cannot write down an explicit well-ordering of reals.
"It is impossible to give an explicit example of a non-Borel-measurable subset of $\mathbb{R}$." math.stackexchange.com/questions/226559/…
"In other words, it is impossible to write down a well-ordering of $\mathbb{R}$ in ZF." math.stackexchange.com/questions/6501/…
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