\begin{frame} \frametitle{Kripke Models: Truth in Worlds} \begin{goal}{} The notation \begin{align*} \mathcal{M},w \;\fc\; \phi \end{align*} means: formula $\phi$ is true in the world $w$ of Kripke model $\mathcal{M}$. \end{goal} \bigskip\bigskip \pause We often abbreviate \begin{talign} \mathcal{M},w \;\fc\; \phi \end{talign} as \begin{talign} w \;\fc\; \phi \end{talign} if the Kripke model $\mathcal{M}$ is clear from the context. \end{frame}