Proofs and Expressiveness in Alethic Modal Logic
نویسندگان
چکیده
The above dictionary characterization of alethic modalities states the central notions of alethic modal logic: necessity, and other notions that are usually thought of as being definable in terms of necessity and Boolean negation: impossibility, contingency, and possibility. The syntax of modal propositional logic is inductively defined over a denumerable set of sentence letters p0, p1, p2, . . . as follows: A ::= p | ¬A | (A ∨B) | 2A
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