Negative Translations and Normal Modality

摘要

We discuss the behaviour of variants of the standard negative translations - Kolmogorov, G?del-Gentzen, Kuroda and Glivenko - in propositional logics with a unary normal modality. More specifically, we address the question whether negative translations as a rule embed faithfully a classical modal logic into its intuitionistic counterpart. As it turns out, even the Kolmogorov translation can go wrong with rather natural modal principles. Nevertheless, we isolate sufficient syntactic criteria ensuring adequacy of well-behaved (or, in our terminology, regular) translations for logics axiomatized with formulas satisfying these criteria, which we call enveloped implications. Furthermore, a large class of computationally relevant modal logics - namely, logics of type inhabitation for applicative functors (a.k.a. idioms) - turns out to validate the modal counterpart of the Double Negation Shift, thus ensuring adequacy of even the Glivenko translation. All our positive results are proved purely syntactically, using the minimal natural deduction system of Bellin, de Paiva and Ritter extended with additional axioms/combinators and hence also allow a direct formalization in a proof assistant (in our case Coq).