Re: Set theory and modal logic

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Article #105

#105

From: Colin Mclarty
Date: Wed, 08 Apr 1992 16:10

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In a previous article, logic@gacvx2.gac.edu () says:

>In article <1992Apr7.124948.5325@vax.oxford.ac.uk>, loader@vax.oxford.ac.uk (R Loader) writes:
>
>> S4 and S5 (and most other common modal logics), are subsystems of classical
>> (non-modal) logic extended with the axiom: A iff \box A.
>
>Other stuff deleted....
>
>> Ralph Loader,
>> Mathematical Institute, Oxford.
>
>S4 and S5 are supersystems, not subsystems, of classical logic..  Neither
>contain the axiom "A iff \box A", both contain the axiom "if \box A then A".
>
>Al Hart
>

I made the same mistake at first.  You have to read Loader's post more
carefully.

Colin McLarty

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References: <1992Apr8.100146.689@gacvx2.gac.edu> <1992Apr5.213320.27618@morrow.stanford.edu> <1992Apr7.124948.5325@vax.oxford.ac.u

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From: cxm7@po.CWRU.Edu (Colin Mclarty)
Subject: Re: Set theory and modal logic
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References: <1992Apr8.100146.689@gacvx2.gac.edu> <1992Apr5.213320.27618@morrow.stanford.edu> <1992Apr7.124948.5325@vax.oxford.ac.u
Date: Wed, 8 Apr 92 16:10:29 GMT
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