[FOM] query about ZFC + (a global choice function)

Aatu Koskensilta Aatu.Koskensilta at uta.fi
Sat Dec 18 21:04:31 EST 2010

Quoting Martin Davis <eipye at pacbell.net>:

> I have received an email message inquiring about a rumor that a proof
> had been announced on FOM that:
> ZFC + (a global choice function) is a conservative extension of ZFC.

   This follows by a simple forcing argument -- using set sized choice  
functions as forcing conditions -- essentially the same way we  
establish NBG with global choice is conservative over ZFC. Here I take  
ZFC + (a global choice function) is ZFC augmented with a function  
symbol posited to choose an element from any non-empty set.

Aatu Koskensilta (aatu.koskensilta at uta.fi)

"Wovon man nicht sprechen kann, darüber muss man schweigen"
  - Ludwig Wittgenstein, Tractatus Logico-Philosophicus

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