EntityQ5128344· pop 6· linked from 7 articlesclassical modal logicSign in to savemodal logic containing the duality axiom schema ◊A↔¬◻¬A as well as the deduction rule A↔B ⊢ ◻A↔◻BConnectionslogicEntityif and only ifEntitymodal logicEntitydualityEntitynormal modal logicEntityCategoriesModal logic