Article View: sci.logic
Article #113Re: Set theory and modal logic
From: R Loader
Date: Fri, 10 Apr 1992 15:17
Date: Fri, 10 Apr 1992 15:17
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1191 bytes
In article <1992Apr8.100146.689@gacvx2.gac.edu>, logic@gacvx2.gac.edu writes: > 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 Sorry, My original posting was ambiguous: I meant ". . . are subsystems of the logic obtained by adding A iff \box A to classical logic" -- Ralph Loader, Oxford.
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Path: arc1-ca.pugleaf.net!sparky!uunet!mcsun!uknet!ox-prg!oxuniv!loader From: loader@vax.oxford.ac.uk (R Loader) Newsgroups: sci.logic Subject: Re: Set theory and modal logic Message-ID: <1992Apr10.161709.5397@vax.oxford.ac.uk> Date: 10 Apr 92 15:17:09 GMT References: <1992Apr5.213320.27618@morrow.stanford.edu> <1992Apr7.124948.5325@vax.oxford.ac.uk> <1992Apr8.100146.689@gacvx2.gac.edu> Organization: Oxford University VAXcluster Lines: 20