An accessibility relation is a relation which plays a key role in assigning truth values to sentences in the relational semantics for modal logic. In relational semantics, a modal formula's truth value at a possible world w {\displaystyle w} can depend on what is true at another possible world v {\displaystyle v} , but only if the accessibility relation R {\displaystyle R} relates w {\displaystyle w} to v {\displaystyle v} .
An accessibility relation is a relation which plays a key role in assigning truth values to sentences in the relational semantics for modal logic. In relational semantics, a modal formula's truth value at a possible world w {\displaystyle w} can depend on what is true at another possible world v {\displaystyle v} , but only if the accessibility relation R {\displaystyle R} relates w {\displaystyle w} to v {\displaystyle v} .
Source: Wikipedia "Accessibility relation" · CC BY-SA 4.0
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