PP200206: Bezhanishvili, Guram and Gehrke, Mai (2002) A New Proof of Completeness of S4 with respect to the Real Line. [Report]

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Abstract
It was proved in McKinsey and Tarski [7] that every finite wellconnected closure algebra is embedded into the closure algebra of the power set of the real line R. Pucket [10] extended this result to all finite connected closure algebras by showing that there exists an open map from R to any finite connected topological space. We simplify his proof considerably by using the correspondence between finite topological spaces and finite quasiordered sets. As a consequence, we obtain that the propositional modal system S4 of Lewis is complete with respect to Boolean combinations of countable unions of convex subsets of R, which is strengthening of McKinsey and Tarski's original result. We also obtain that the propositional modal system Grz of Grzegorczyk is complete with respect to Boolean combinations of open subsets of R. Finally, we show that McKinsey and Tarski's result can not be extended to countable connected closure algebras by proving that no countable Alexandroff space containing an infinite ascending chain is an open image of R.
Item Type:  Report 

Report Nr:  PP200206 
Series Name:  Prepublication (PP) Series 
Year:  2002 
Uncontrolled Keywords:  modal logic, topological completeness, real line, Alexandroff space 
Subjects:  Logic 
Date Deposited:  12 Oct 2016 14:36 
Last Modified:  12 Oct 2016 14:36 
URI:  https://eprints.illc.uva.nl/id/eprint/70 
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