Classical modal logic: Difference between revisions

Revision as of 16:31, 28 April 2020

Revision as of 16:19, 20 December 2020

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<math>\Diamond A \equiv \lnot\Box\lnot A</math>

whichthat is also [[Deductive closure|closed]] under the rule

<math> A \equiv B \vdash \Box A\equiv\Box B.</math>

Alternatively one can give a dual definition of '''L''' by which '''L''' is classical [[iffif and only if]] it contains (as axiom or theorem)

<math>\Box A \equiv \lnot\Diamond\lnot A</math>