Dual-context calculi for modal logic

We show how to derive natural deduction systems for the necessity fragment of various constructive modal logics by exploiting a pattern found in sequent calculi. The resulting systems are dual-context systems, in the style pioneered by Girard, Barber, Plotkin, Pfenning, Davies, and others. This amounts to a full extension of the Curry-Howard-Lambek correspondence to the necessity fragments of a constructive variant of the modal logics K, K4, GL, T, and S4. We investigate the metatheory of these calculi, as well as their categorical semantics. Finally, we speculate on their computational interpretation.