\begin{frame}[t] \begin{block}{} \begin{center} $\begin{array}{llcl} (1)&e\cdot x&\to&x\\ (2)&I(x)\cdot x&\to&e\\ (3)&(x\cdot y)\cdot z &\to& x\cdot (y\cdot z)\\ (4)&I(x)\cdot (x\cdot z)&\to& z\\ (5)&I(e)\cdot z&\to& z \end{array}$ \end{center} \end{block} \bigskip Overlap between rules (4) and (2) with critical pair: \bigskip\pause \begin{center} \begin{tikzpicture}[very thick,->] \node (t) {$I(I(y))\cdot (I(y)\cdot y)$}; \node (l) [below left=of t] {$I(I(y))\cdot e$}; \node (r) [below right=of t] {$y$}; \draw (t) -- (l) node [midway,above left] {$2$}; \draw (t) -- (r) node [midway,above right] {$4$}; \onslide<3->{\draw [dashed] (l) -- (r) node [midway,above] {$6$};} \end{tikzpicture} \end{center} \pause Add a rule: \begin{block}{} (6)\hspace{2em} $I(I(y))\cdot e\to y$ \end{block} \end{frame}