\begin{frame}{Encoding a PCP-Instance into a Formula} \begin{center} \scalebox{.8}{ \begin{minipage}{\textwidth} \understandmodel{} \end{minipage} } \end{center} \pause\smallskip \begin{goal}{} Interpreting $\aformi{3} \defdby \formula{\existsst{z}{\:\binpred{P}{z}{z}}}$ in $\amodel$ we find: \pause \begin{align*} \amodel \satisfieslookup{\saluf} \aformi{3} \mpause[1]{ \;\;&\Longleftrightarrow\;\; \text{there is a $w\in\model{B}$ such that $\pair{w}{w} \in \intin{\sbinpred{P}}{\amodel}$} } \\ \mpause{ \;\;&\Longleftrightarrow\;\; \parbox[t]{0.7\textwidth}{ there is a sequence \!$\tuple{i_1,i_2,\ldots,i_n}$\! of indices\\ such that $\forestgreen{w}_{i_1}\forestgreen{w}_{i_2}\cdots \forestgreen{w}_{i_n} = \forestgreen{v}_{i_1}\forestgreen{v}_{i_2}\cdots \forestgreen{v}_{i_n}$} } \\ \mpause{ \;\;&\Longleftrightarrow\;\; \text{PCP instance $\forestgreen{I}$ is solvable} } \end{align*} \end{goal} \vspace{10cm} \end{frame}