Abstract
We prove that a natural and simple predicate modal logic with the Barcan formula, namely QBF-KD plus the axiom of density, is not Kripke complete. Although incompleteness results are known in Kripke semantics, most of the methods used can only apply to logics stronger than QBF-S4 as they are based in a translation from intermediate logics. We give here an original proof of this incompleteness result.
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