 Various semantics have been developed in which deontic terms are applied directly to actions, conceived as transitions between states in a Kripke-model. For instance, following the reduction of SDL to alethic modal logic (cf.  Section 3),  Meyer 1988 adds an Andersonian “violation” constant V to  propositional dynamic logic  (PDL). In this framework, [\(\alpha\)]V expresses that executing the action \(\alpha\) necessarily leads to a violation, hence, “\(\alpha\) is forbidden”. Where \(-\alpha\) denotes the negation of action \(\alpha\), [\(-\alpha\)]V then represents that \(\alpha\) is  obligatory.[82]  Note that intuitively, this formula can be read as: “whenever \(\alpha\) is not carried out, a violation occurs”. Alternatively, one may define a notion of strong permissibility of an action \(\alpha\), by introducing a Kangerian constant “OK” and expressing that \(\alpha\) is strongly permissible by [\(\alpha\)]OK. This means, intuitively, that whenever one executes the action \(\alpha\), then one is guaranteed to end up in a world that is deontically acceptable (no violation  occurs).[83]