Logic Journal of IGPL Advance Access originally published online on August 4, 2009
Logic Journal of IGPL 2009 17(6):719-754; doi:10.1093/jigpal/jzp029
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Independence-friendly cylindric set algebras
IHPST (Paris 1/CNRS/ENS), 13 rue du Four, 75006 Paris, France.
E-mail: allen.l.mann{at}gmail.com
| Abstract |
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Independence-friendly logic (IF logic) is a conservative extension of first-order logic that has the same expressive power as existential second-order logic. We attempt to algebraize IF logic in the same spirit as cylindric algebra.
We define independence-friendly cylindric set algebras (IF algebras) and investigate to what extent they satisfy the axioms of cylindric algebra. We ask whether the equational theory of IF algebras is finitely axiomatizable, and prove two partial results. First, every IF algebra over a structure is an expansion of a Kleene algebra. Moreover, the class of such Kleene algebras generates the variety of all Kleene algebras. Second, every one-dimensional IF algebra over a structure is an expansion of a monadic Kleene algebra. However, the class of such monadic Kleene algebras does not generate the variety of all monadic Kleene algebras.1
Key Words: independence-friendly logic cylindric algebra De Morgan algebra monadic De Morgan algebra
Received for publication 21 October 2007.
1Revisions to the present paper were supported by the European Science Foundation collaborative research project Logic for Interaction (LINT).