\begin{frame}{Model Informally (1)} \begin{exampleblock}{} \vspace{-1ex} \begin{talign} \formula{\existsst{x}{\,\unpred{P}{x}}} \end{talign} \pause% If we interpret $\formula{\unpred{P}{x}}$ as `\sentence{\black{$x$} is green}', this expresses: \begin{scenter} There is something that is green. \end{scenter} \pause\smallskip This formula has a \emph{model}: \begin{itemize} \item universe $\{1,2,3\}$ \item $\unpred{P}{1}$,\; $\lognot{\unpred{P}{2}}$,\; $\lognot{\unpred{P}{3}}$ \end{itemize} \medskip \pause In a picture, this looks as follows: \begin{scenter} \begin{tikzpicture}[dot/.style={minimum size=4mm, circle, draw=none, fill=black, inner sep=0, outer sep=1mm, text=white}] \node [dot,fill=forestgreen] (1) {1}; \node [dot,below right of=1] (2) {2}; \node [dot,above right of=2] (3) {3}; % \draw [rounded corners=5mm,thick,dashed] ($(1) + (-6mm,7mm)$) rectangle ($(3) + (6mm,-13mm)$); \end{tikzpicture} \end{scenter} A \forestgreen{green dot} indicates that $\sunpred{P}$ is $\T$. \end{exampleblock} \end{frame}