🌐EnglishEnglishEspañolItalianoPortuguêsРусскийفارسیEntityQ5128344· pop 6· linked from 7 articlesclassical modal logicmodal logic containing the duality axiom schema ◊A↔¬◻¬A as well as the deduction rule A↔B ⊢ ◻A↔◻BAvailable in 6 languagesРусскийPortuguêsItalianoLatinفارسیvia Wikidata sitelinks · CC0ConnectionslogicEntityif and only ifEntityCategoriesModal logic