Embedding Intuitionistic into Classical Logic

The famous double negation translation [16, 17] establishes an embedding of classical into intuitionistic logic. Curiously, the reverse direction has not been covered in literature. Utilizing a normal form for intuitionistic logic [20], we establish a small model property for intuitionistic propositional logic. We use this property for a direct encoding of the Kripke semantics into classical propositional logic and quantified Boolean formulae. Next, we transfer the developed techniques to the first order case and provide an embedding of intuitionistic first-order logic into classical first-order-logic. Our goal here is an encoding that facilitates the use of state-of-the-art provers for classical first-order logic for deter- mining intuitionistic validity. In an experimental evaluation, we show that our approach can compete with state-of-the-art provers for certain classes of benchmarks, in particular when the intuitionistic content is low. We further note that our constructions support the transfer of counter-models to validity, which is a desired feature in model checking applications.