In some systems of modal logic, a unary operator $A$ on formulae sometimes included that corresponds to the modality ‘in the actual world, $\phi$ is true’. Some presentations of semantics for modal logics sometimes include a distinguished possible world $w_{@}$ that is intended to stand in for the actual world. In such cases, the truth conditions for the operator $A$ are:

• • $\text{A}\phi$ is true at a world $w$ if and only if $\phi$ is true at $w_{@}$.