[FOM] Tolerance Principle (re assertions made about Con(NF))

Lew Gordeew legor at gmx.de
Wed Feb 15 18:11:52 EST 2006

Randall Holmes wrote on Tue, 14 Feb 2006 16:07:48 -0700:
> There is _nothing_ to indicate that NF is any stronger than the simple
> theory of types with the Axiom of Infinity 

Proof Theory is the crucial indication. Because cut elimination in TT+Inf,
as well as NFU+Inf, is known and not very hard. Not in NF though. As I
already pointed out, cut elimination in full NF, i.e. including Ext, is
troublesome. Also note that Ext proves Inf in NF.

L. Gordeev

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