classical modal logic
modal logic containing the duality axiom schema ◊A↔¬◻¬A as well as the deduction rule A↔B ⊢ ◻A↔◻B
regular modal logic
modal logic containing the duality axiom schema ◊A↔¬◻¬A as well as the deduction rule (A∧B)→C ⊢ (◻A∧◻B)→◻C
modal logic containing the duality axiom schema ◊A↔¬◻¬A as well as the deduction rule A↔B ⊢ ◻A↔◻B