[FOM] question

[Robert Lubarsky]

I never heard of this before, but if you want a proof:

Let P be a sentence in which the quantifiers range over N. Suppose ZF + AC +
GCH proves P. Let M be a model of ZF. We want to show P is true in M.

P holds in M iff P holds in L^M, which it does, because L^M models ZF + AC +
GCH.

Bob Lubarsky


-----Original Message-----
From: fom-bounces at cs.nyu.edu [mailto:fom-bounces at cs.nyu.edu] On Behalf Of
Roman Murawski
Sent: Friday, May 22, 2015 3:38 AM
To: fom at cs.nyu.edu
Subject: [FOM] question



Dear FOMers,

I was told about  Kreisel's result stating that ZF + AC + GCH is a
conservative extension of ZF with respect to sentences about natural
numbers. Is it true? Where one can find it?

Best

Roman Murawski


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