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diff --git a/vorlesungen/slides/3/wurzel2.tex b/vorlesungen/slides/3/wurzel2.tex
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+%
+% wurzel2.tex
+%
+% (c) 2021 Prof Dr Andreas Müller, OST Ostschweizer Fachhochschule
+%
+\begin{frame}[t]
+\setlength{\abovedisplayskip}{5pt}
+\setlength{\belowdisplayskip}{5pt}
+\frametitle{$\mathbb{Z}(\sqrt{2})\only<7->{ = \mathbb{Z}[X]/(X^2-2)}$}
+\vspace{-20pt}
+\begin{columns}[t,onlytextwidth]
+\begin{column}{0.48\textwidth}
+\begin{block}{Der Ring $\mathbb{Z}(\sqrt{2})$}
+$\mathbb{Z}(\sqrt{2})$ als Teilring:
+{\color{blue}
+\[
+R=\{ a+b\sqrt{2}\;|\; a,b\in\mathbb{Z} \} \subset \mathbb{R}
+\]}%
+\uncover<2->{$\sqrt{2}\not\in\mathbb{Q}$}\uncover<3->{
+$\Rightarrow$
+$1$ und $\sqrt{2}$ sind inkommensurabel}\uncover<4->{
+$\Rightarrow$
+$R$ dicht in $\mathbb{R}$}
+\end{block}
+\uncover<5->{%
+\begin{block}{Algebraische Konstruktion}
+\uncover<8->{%
+Das Polynom $X^2-2$ ist irreduzibel als Polynom in $\mathbb{Q}[X]$}
+\[
+\uncover<8->{\mathbb{Z}[X]/(X^2-2)
+=}
+{\color{red}\{a+bX\;|\;a,b\in\mathbb{Z}\}}
+\]\uncover<7->{%
+mit Rechenregel: $X^2=2$}
+\end{block}}
+\end{column}
+\begin{column}{0.48\textwidth}
+\begin{center}
+\begin{tikzpicture}[>=latex,thick,scale=0.92]
+\begin{scope}
+\clip (-3.2,-3.2) rectangle (3.2,3.2);
+\foreach \x in {-10,...,10}{
+	\pgfmathparse{int(\x/sqrt(2))-5}
+	\xdef\s{\pgfmathresult}
+	\pgfmathparse{int(\x/sqrt(2))+5}
+	\xdef\t{\pgfmathresult}
+	\foreach \y in {\s,...,\t}{
+		\uncover<4->{
+			\fill[color=blue] ({\x-\y*sqrt(2)},0)
+				circle[radius=0.05];
+		}
+		\uncover<6->{
+			\draw[color=blue,line width=0.1pt] 
+				({\x-\y*sqrt(2)-3.2},3.2) 
+				--
+				({\x-\y*sqrt(2)+3.2},-3.2);
+		}
+	}
+}
+\end{scope}
+
+\draw[->] (-3.2,0) -- (3.5,0) coordinate[label={$\mathbb{Z}$}];
+
+\uncover<5->{
+	\draw[->] (0,-3.2) -- (0,3.5) coordinate[label={right:$\mathbb{Z}X$}];
+
+	\foreach \x in {-3,...,3}{
+		\foreach \y in {-2,...,2}{
+			\fill[color=red]
+				({\x},{\y*sqrt(2)}) circle[radius=0.08];
+		}
+	}
+}
+
+\end{tikzpicture}
+\end{center}
+\end{column}
+\end{columns}
+\end{frame}