Kripke models

A form of Kripke model — A Kripke frame together with any one of the following: (1) a function associating each of the frame's worlds to a set of prime formulae which are "true" for the given world, (2) a function associating each prime formula to a set of worlds for which the prime formula is "true", (3) a forcing relation between worlds and prime formulae. Additionally, there is a set of rules for deducing (from the given function or relation) what formulae are forced to be true by a given world. (The set of rules depends on which logic the Kripke model is being applied to, whether one of several modal logics or intuitionistic logic). For intuitionistic logic the forcing relation satisfies a persistence relation, namely, if world w forces proposition p, then all worlds accessible from w also force p.