SHAWN MICHAEL STANDEFER2021-11-262021-11-2620180039-32151572-8730https://scholars.lib.ntu.edu.tw/handle/123456789/587923We present some proof-theoretic results for the normal modal logic whose characteristic axiom is ∼ □ A≡ □ ∼ A. We present a sequent system for this logic and a hypersequent system for its first-order form and show that these are equivalent to Hilbert-style axiomatizations. We show that the question of validity for these logics reduces to that of classical tautologyhood and first-order logical truth, respectively. We close by proving equivalences with a Fitch-style proof system for revision theory.Functional modal logic | Hypersequents | Proof theory | Revision theory[SDGs]SDG16journal article10.1007/s11225-017-9725-02-s2.0-85020739959https://doi.org/10.1007/s11225-017-9725-035764125