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Nov 11, 2022 at 19:07 comment added Noah Schweber As a very-belated comment, I think that your argument also shows independent axiomatizability for second-order logic in higher-order languages; since interpolation fails in that setting, Reznikoff's original argument doesn't trivially go through.
Mar 16, 2022 at 23:26 history bounty ended Noah Schweber
Mar 16, 2022 at 14:38 comment added Emil Jeřábek I see. I didn’t really study the proof in detail.
Mar 16, 2022 at 14:34 vote accept Noah Schweber
Mar 16, 2022 at 14:34 history edited Emil Jeřábek CC BY-SA 4.0
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Mar 16, 2022 at 14:34 comment added Noah Schweber Doesn't Reznikoff use compactness? (Or did I have a fascinating logic hallucination, as one sometimes does?) BTW I can't award the bounty for another 3 hours, but as soon as I can I will. Thanks as always!
Mar 16, 2022 at 14:33 comment added Emil Jeřábek Ah, ok, you are right. I didn’t really think about it, and assumed there was a problem with it, as this is the only sophisticated property of first-order logic used in Reznikoff’s proof. So why doesn’t Reznikoff’s proof apply to second-order logic?
Mar 16, 2022 at 14:24 comment added Noah Schweber This is nice, and I think it works! A quick question: you say Craig isn't available in SOL, but isn't it trivialy true in SOL since we can directly quantify over the "extra symbols" in the interpolant?
Mar 16, 2022 at 13:53 history edited Emil Jeřábek CC BY-SA 4.0
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Mar 16, 2022 at 13:46 history edited Emil Jeřábek CC BY-SA 4.0
added 198 characters in body
Mar 16, 2022 at 13:33 history answered Emil Jeřábek CC BY-SA 4.0