Article View: sci.logic
Article #558Re: recursive definitions and paradoxes
From: Vaughan R. Pratt
Date: Fri, 20 Nov 1992 17:52
Date: Fri, 20 Nov 1992 17:52
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1758 bytes
In article <1992Nov20.155725.11719@guinness.idbsu.edu> holmes@garnet.idbsu.edu (Randall Holmes) writes: >>Russell's paradox denies the existence of the paradoxical set of all >>sets. Denial of an existential is a universal, and the universal >>statement asserted by Russell's paradox is that every set has a >>nonmember. The universal set is "too big" by one element, having no >>nonmember. From that perspective size has everything to do with it. >>-- >>Vaughan Pratt A fallacy is worth a thousand steps. > >This is inaccurate. Russell's paradox proves nothing except that >there is no set which has exactly the sets which are not elements of >themselves as members. If the Axiom of Separation is added to one's >theory, the paradox has the consequence indicated. In theories where >the Axiom of Separation does not hold (like NFU) the paradox has >different consequences. Good point, I hadn't spent long enough thinking about the meaning of David Gudeman's "What if you altered ZF to contain this axiom (and introduction of definitions)?" I guess this must entail dropping Separation, right? -- Vaughan Pratt A fallacy is worth a thousand steps.
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Newsgroups: sci.logic Path: arc1-ca.pugleaf.net!sparky!uunet!stanford.edu!CSD-NewsHost.Stanford.EDU!Sunburn.Stanford.EDU!pratt From: pratt@Sunburn.Stanford.EDU (Vaughan R. Pratt) Subject: Re: recursive definitions and paradoxes Message-ID: <1992Nov20.175227.13147@CSD-NewsHost.Stanford.EDU> Sender: news@CSD-NewsHost.Stanford.EDU Organization: Computer Science Department, Stanford University. References: <26788@optima.cs.arizona.edu> <1992Nov19.215048.26539@CSD-NewsHost.Stanford.EDU> <1992Nov20.155725.11719@guinness.idbsu.edu> Date: Fri, 20 Nov 1992 17:52:27 GMT Lines: 22