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Minimal predicates, fixed-points, and definability

Published online by Cambridge University Press:  12 March 2014

Johan Van Benthem*
Affiliation:
Institute for Logic, Language and Computation Illc, Universiteit Van Amsterdam, Plantage Muidergracht 24, 1018 TV Amsterdam, The NederlandsE-mail:, johan@science.uva.nlDepartment of Philosophy, Stanford University, Stanford. CA 94305-2155., USAE-mail:, johan@science.uva.nl

Abstract

Minimal predicates P satisfying a given first-order description ϕ(P) occur widely in mathematical logic and computer science. We give an explicit first-order syntax for special first-order ‘PIA conditions’ ϕ(P) which guarantees unique existence of such minimal predicates. Our main technical result is a preservation theorem showing PIA-conditions to be expressively complete for all those first-order formulas that are preserved under a natural model-theoretic operation of ‘predicate intersection’. Next, we show how iterated predicate minimization on PIA-conditions yields a language MIN(FO) equal in expressive power to LFP(FO), first-order logic closed under smallest fixed-points for monotone operations. As a concrete illustration of these notions, we show how our sort of predicate minimization extends the usual frame correspondence theory of modal logic, leading to a proper hierarchy of modal axioms: first-order-definable, first-order fixed-point definable, and beyond.

Information

Type
Research Article
Copyright
Copyright © Association for Symbolic Logic 2005

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